Even when something exists in a manufacturers N gauge range it seems to be a pain to actually get them lately due to lack of reruns of older releases.
The Farish Black 5 is a prime example - hardly ever see any for sale.
Sometimes seems like theres two extremes with N, either it sells like hotcakes and if you aren't there at release you'll miss it and be up the creek or it doesn't sell at all and ends up in the bargain bin for no real reason. Distinct lack of a middle ground where a newcomer can come in and find some models of fairly common prototypes.
I've been on the lookout for blue/grey MK1's to make up a fake 4TC rake, so far managed to find an FK and thats it...lol