I just wanna drop this in the bucket to maybe inspire students. There are many ways to skin a cat in engineering. Sometimes we become too tunnel visioned when we can't get something.
Andymark doesn't have the TIRES and TUBES. but you know what, that is a pretty common size you can just about get anywhere else.
Andymark has the HUB instock, that is the best part. Purchase the hubs you need then maybe look somewhere else for the tire and tube. It's a metric size of 200 x 50 is the tire you are looking for. In some cases, they even sell FOAM FILLED tires. Here is a link to eBay with numerous choices.
You can atleast buy some eBay tires to test your proto-typing to buy you some "time" if you really want the kewl Andymark brand.
http://www.ebay.com/sch/i.html?_from...ire&_sacat= 0
Happy shopping and sourcing...
EDIT...well YESTERDAY Andymark had hubs in stock...not today...LOL... Oh well....I tried.