It depends a lot on how current it is, I just replaced the tires on an old mobil crane by buying the tires being used for the Chameleon set. They aren't an exact fit, being a little bit narrower, but they fit the wheel hub fine which is what matters most. The part number was identical but I think they have actually made newer molds since the part was first used decades ago.
You can start at PlaymoDB with a search like
This OneThen find what size you need and see if there is a recent set that has used it. If there is it can probably be ordered from Parts.
To generally confirm availability you enter the part number at the ETN search on Playmobil.de if they have it there then there is a chance to get it. Go to the main playmobil.de page and then at the bottom find the link named "Ersatzteile finden" enter the part number with no spaces in the box in the pop up window and it will let you know if it's available.
If they don't list it then it is unlikely. It is worth a try through US Parts though since they sometimes still have things that have disappeared form parts Germany.