I gave up on the spacers. The case is still tight without them and I have not noticed any problems. I think they mainly serve to line up the keyboard assembly with the case when you screw them together, but it seems the keyboard will be fine without them. The assembled keyboard is still tight and sturdy during use without the spacers.
If the feet require a higher quality, higher priced alternative, I am not opposed to paying the higher costs, whatever they may be.