Geoff Gooderham resin car kits used to be sold through Central Hobbies (Vancouver). However, that store has closed, so the only way to get them now is to contact Geoff directly (by way of his "Angus Shops" alias on The Railwire)
Note that the photograph above is just a stand-in and not the actual Gooderham model (although it is a Big Otis). If you have a picture of the real thing, do please send it to me.
The CPR built 1225 of these 70-ton "Big Otis" dumping gondolas between 1923 and 1930. They had a capacity of 2627 cu. ft. and were generally used for hauling coal, coke, gypsum and occasionally woodchips. 1158 Big Otis cars were still in service in 1958 and, remarkably, 80 were still listed in the 1972 Official Railway Equipment Register.