My first trade price list is dated 5th January 1976 and this is followed by one dated 4th August 1976. These go together with a Trade Preview Catalogue in black and white.

This was followed by a 1977 Preview Catalogue again in black and white with a price list dated July 18th 1977.

1978 ditto with two price lists dated February 1978 in red and July 1978 in blue.

1979:  Just price lists dated January 1979 in blue and July 1979 on pink paper. The 1979 catalogue was also available to shops with a hard cover and plastic spline. I was told this was so that it could be left for customer perusal.

1980: There are two versions of the catalogue. I understand because of a complaint there was an additional overprint on page 17 of a later version. This stated " N.B. The above model is assembled using components from an M & L white metal kit.". This refers to the illustration of 37079 Manor 7812 'Erlestoke Manor' in BR black.
 

I wrote to the company asking for a retail price list and received a reply that they didn't supply such things. I then found one dated January 1980 together with the later version of the catalogue.

1983: A leaflet was issued entitled Limited Availability Locomotives, with Limited Availability Wagons on the other side. This is dated 1/83. Also in 1983 there were offers of free trips on a series of preserved railways.

Finally 1984:  In the main Palitoy catalogue there were 4 pages for Mainline Railways.   The full range available is shown in the price list which accompanied this catalogue.

I have now found a few minutes to check out the Airfix catalogues/price lists.

1980 - A trade version of the 4th catalogue was produced and issued at the Toy Fairs.   Obviously it had been a rush job and hadn't been checked OR there were some changes in the stock numbers.   A revised version was issued in June together with a retail price list.   The differences are: page 3 stock numbers for Dean Goods 54155-6 in Jan - 54156-9 in Jun, N.2. 0-6-2T L.N.E.R. 54157-2 in Jan - 54154-3 in Jun.   Page 13 Siphon 'H' G.W.R. 54306-2 in Jan - 54308-8 in Jun, Siphon 'G' B.R. 54309-1 in Jan - 54307-5 in Jun.   Page 15  B.R. 60' Suburban 'B' Bow Ended 542257-1 in Jan, 54257-1 in Jun (obviously just a misprint).   The price list matches the June edition.

For the 1981 Toy Fairs there was a loose leaf section in the trade catalogue. This featured gimmick sets such as:

37028 - Branch Freight Nite (sic) Glow Set - which was to have a G.W.R. 0-4-2T with 3 private owner open wagons, a circle of track and battery controller.   "And, to add further excitement, just switch out the lights and see the luminous Nite Glow ore glowing as the train travels around the track."   This achieved with special loads of 'Nite Glow' ore.  

37029 - Diesel Freight Express - "the A1A diesel operating pipe loader which unloads pipes down the ramp one at a time by remote control.   Contents: A1A-A1A Diesel (in blue), 2 wagons (bogie well wagons - Crocodile H in GW grey), oval of track, re-railer, operating pipe loader set, mains controller (Mainline Railways), power connecting clip."

37030 - Steam Logging Set - "The new remote control log loader is featured in this log-hauling freight set.   The versatile Fowler locomotive is at the head of this powerful bogie bolster train.   Contents: 4F Fowler LMS black, 2 bogie bolsters (GW), oval of track, re-railer, remote controlled log loader with logs, mains power controller (Mainline Railways), power connecting clips."

37031 - Diesel Haulage - "The powerful warship diesel with electronic sound klaxon and working headlights heads up this diesel haulage set.   The 4 unit set features a nite-glow bridge that glows in the dark, oval of track, re-railer and mains controller (Mainline Railways)."

37032 - Cornish Riviera Express - "This deluxe set is headed by the Castle Class locomotive with realistic electronic steam sound and whistle.   With 2 coaches, the train travels through an automatic operating crossing gate which lowers as the train approaches and rises when clear.   Contents: Castle Castle Class locomotive with electronic sound and whistle, 2 coaches, oval of track, automatic level crossing, trackside warning sign, mains controller (Mainline Railways), power connecting clips.

37033 - Power Freight Terminal - "This action packed diesel haulage set has the popular A1A-A1A diesel working with the giant crane to load steel girders.   The giant gantry cranes moves side to side, rotates 360 degrees, boom raises and lowers, magnetic hook and line moves up and down and is exciting fun to operate.   Also featured in this mighty set is the operating pipe loader which unloads pipes down the ramp one at a time by remote control.   Contents: A1A-A1A Diesel (blue), 2 bogie bolsters (GW), 2 bogie well wagons, operating crane, girders and unloading area, operating pipe loader and 4 pipes, oval of track, mains controller (Mainline Railways), power connecting clips.

 

Note the Mainline Railways series of stock numbers but these are all under the GMR label and were in the Airfix trade catalogue

There was also a January 1981 trade price list which contains the full range from 1980 at the same retail prices but NO prices for the sets quoted above.