There are plenty of the standard size 35mm available on Ebay other than that you may have to go to something like PCB spacers for circuit boards they come in 50mm or manufacture you own custom sizes with a bit of Aluminum rod and a drill press.
These I have are 35mm tall. They need to be about 10mm taller so I think the best thing to do is get a different frame. I have found one I think will work with the stack I want. I am waiting on confirmation of the max height it can accommodate.
@Tony They are for the frame. As Admiral stated, I may end up having to make my own. I can get some 5mm round aluminum stock and drill/tap my own. However, they will look horrible.