That particular model that you're talking about doesn't appear to be made any more, and nor does the transmitter. So this is obviously going to mean that you can't buy one from new. If you know what you're doing any you're able to figure out how the writing works on the current receiver that you're using, then there's no reason to say why you can't just wire around it. The new ones that will be mounted in at the ceiling would work alright. The worst case scenario that you're looking at is having to replace the face with a remote that's built in.
If this won't work for you, however, then you could perhaps look around a few online stores to try and find the model that you need. Places like eBay could help you, no doubt. By just searching on the eBay website you will be given access to many different kinds of model. You may find the exact model that you were looking for, but you may even find another that could be compatible with the system you have in place already.
If you have a receipt from when you purchased the system then there's nothing stopping you taking it back to the store you purchased it from. If it came with a warranty, too, then you should be able to take it back to the store and either request a refund or a new model. If they give you a refund then you can always just go about purchasing a whole new system which will significantly reduce your problems in the future, as you will more easily be able to find parts when it finally leaves its warranty period. If they give you a replacement part then you shouldn't have anything to worry about either.
If this won't work for you, however, then you could perhaps look around a few online stores to try and find the model that you need. Places like eBay could help you, no doubt. By just searching on the eBay website you will be given access to many different kinds of model. You may find the exact model that you were looking for, but you may even find another that could be compatible with the system you have in place already.
If you have a receipt from when you purchased the system then there's nothing stopping you taking it back to the store you purchased it from. If it came with a warranty, too, then you should be able to take it back to the store and either request a refund or a new model. If they give you a refund then you can always just go about purchasing a whole new system which will significantly reduce your problems in the future, as you will more easily be able to find parts when it finally leaves its warranty period. If they give you a replacement part then you shouldn't have anything to worry about either.