Try an hub from AndyMark, they bolt on to all of the AM wheels [including kit].
They have options for keys and hex.
I would NOT use a press fit for a drive wheel.
If you give us more details on what this is for, we can help you more.
Have you considered driving with a dead axle? This is like the kit bot if your team took the time to look at that. Basically a wheel has bearings on it that allow it to rotate freely about its axle with very little friction. Then you can bolt sprockets (or gears) to the wheel itself and drive that sprocket with chain running from the motor (or other gears). This may be easier to do/easier to find with limited resources.
For live axles where the axles actually drive the wheels, many teams use hex shafts. This might be tough to do with limited resources, but the COTS stuff is out there.
If you wanted to do a live axel, you could order long hex output shafts from andy mark and run the axel through your frame with a hex bearing block holding the other end, but really, dead axels with chain and sprockets gives you more flexibility for gear ratios and it’s alot easier with limited resources. http://www.andymark.com/product-p/am-0396.htm- these just drop right into the andy mark toughbox minis (if that is what you’re using)