You could try registering as a rabbit - otherwise same details but as a cat if it doesn't work?
I have lots of animals (rabbits, cats, dogs) so I don't really have this issue as they are all registered - maybe someone else can advise.
Panacur 10% is regularly used for rabbits - and cheaper and easier to dose accurately compared to the 'rabbit' syringes. There shouldn't be too much of an issue. I've also bought it from an equine supplier and I'm sure I said it was for rabbits.