Forty years ago I bought a Heller HO/OO railway accessory. Heller discontinued the kit but after several years of searching I found that Knightwing took it over.
http://www.knightwing.co.ukDespite being for HO/OO - or 1/72nd, most of it looked good for 1/48th & 1/35th. I have been using these for a few years for 1/35th cargo in trucks and they’ve proved great.
Each sprue has 2 large crates, 5 small crates, 3 each large, small & little cable-reels, 10 flour sacks, 5 wood barrels, 6 small oil drums, 3 duckboards(?), 10 crates of bottles (which I use as 1/35th bullets in boxes) & 20 small rectangular shapes (which I use as small ammo boxes).
Knightwing warn that (due to a family death & Eastern production costs) they may not be able to continue so act now if you want them. Search around for the best price & check how many sprues you get for your money – some are sold separately, some in double or triple packs.
Large crates are 20 x 18 & 14mm H
Small crates are 10mm square & 16mm H
Wood barrels are 10mm dia x 13mm H
Found these two suppliers. Kit numbers are PM101 (single sprue), kit PM139 (double pack), PM108 (triple pack).
http://www.knightwing.co.uk/cgi-bin/commerce.cgi?cart_id=1656707729.326&product=OO-HO_Building_Kits&pid=271https://www.romancart.com/search.asp?storeid=46708&searchterm=crates
