I can't vouch for them as I haven't ordered yet (am looking for tires too) but I found the following:
-
ToyResto.com (they don't have the size I need but might have yours)
- This
eBay store seems to have a selection and offers front+rear 'sets' which is cool when they are different styles/sizes.
There are a couple of others in the Europe and Australia too, just Google "
Matchbox replacement parts" or "
Matchbox restoration parts".
TIP: It's the plastic wheel that shrinks making the tire loose (or fall off) so the new ones may be loose too. Whether new or old I've found that a small bead of clear silicone adhesive/sealer applied with a toothpick around the inside of the tire is easiest to work with. It fills in the gap nicely, the excess wipes off easily, it blends in well when dry (it's shiny like the tires), plus it also can be removed later if needed. Don't let the vehicle rest on its wheels while it sets up and drys to keep everything straight.