How do I find replacement front casters for vacuum cart?

I'm trying to fix the front casters on a cart for a Craftsman 16 gallon wet/dry vacuum. The vacuum is model #113179930. Sears has a very helpful exploded view diagram for the product:

http://www.searspartsdirect.com/model-nu...

The casters I need are #23, Parts #: 73237. However, it seems they're no longer available, at least from Sears:

http://www.searspartsdirect.com/part-num...

Sears no-so-helpfully suggests: "The manufacturer no long makes this part, and there's no substitute part. If you choose to purchase a new product, please visit www.sears.com"

The current casters I believe have a completely missing roller bearing and therefore no longer will stay upright:

The casters slide into these attachments on the front of the vacuum cart:

Any advice to:

1) Find the exact replacement part

2) Find a suitable replacement I can install with the existing mounts

3) Come up with an entirely new wheel and mount system to pull wheels back on the front of the cart.

Thanks!