i had the same problem--i think you can use the parts from the Strida--look at them carefully check out this strida number for parts 800 783 5683--parts for the microbike are just not available - i changed the pneumatic tires for solid ones like on motorized wheelchairs impossible to get on but the wheelchair people have a way to do it--no more flats but did add weight to the bike--i did have a metal spoked wheel rim made for the bike--cost $125.00 but added no advantage--easy to fill with air but the tires are a disaster--ps i think you can get a rear hub and wheel--once again check out the strida for parts
let me know what happens
plener@gmail.com