Old Victorian sets like that bathroom are very popular among collectors, so it might be difficult getting these specific parts for a low price.
Depending on where you're located, you can also get lucky on national websites for second-hand stuff to buy and to sell. It's a bit of a hunt, but it's very satisfactory when old used Playmobil turns up for a low price. Since you only need a few spare parts, the set doesn't have to be in very good condition.
For instance, I live in Belgium and I sometimes find good deals on
http://www.2dehands.be from parents selling old Playmobil their kids don't use anymore.
Good luck!