If you can't get a spare part from Tamiya, you can make a copy of one of the existing wheels using Oyumaru mold material that you stick in boiling water along with some miliput or green stuff
Since you really just need to open face side it is very easy. Boil some water, drop the Oyumaru in it for 30 seconds or so, squish it around an existing part and let it cool
mix i[ some milliput or green stuff and press it into the mold. Let it dry and viola, you've got a copy of your part
There are lots of videos on using Oyumaru
I did it for this tiger sprocket part on my 1/72 Y-Wing for example
View attachment 98623
I have even done two part molds with the Oyumaru stuff to make copies of pilots or more complex parts, but those are a bit harder to do