Need Info On Reamers

I'm trying to figure out how and where to buy reamers. I need to
create some 5/8" and 1/2" holes in ultra high molecular weight
polyethylene blocks for my control system. The aileron push tubes
slide thorugh the blocks and the aileron actuators mount in the blocks
as well. The mounting component of my aileron actuator is 5/8", so
when buying the .6250" reamer is that already slightly oversized? I
have been told the holes should be oversized by .002". I have looked
for reamers on line but don't know if what I'm buying is the right
size, there is little or no description for them.

Can someone tell me what I should look for in buying these tools and
where may be the best place to do so?

Thanks. Don