Did anyone mention to you that a Dremel rotary tool fits that stock spindle holder? If you happen to have a Dremel laying around you might want to try that. I really enjoyed cutting with it but it takes 1/8" bits max (although you could get an adapter). Might get you by. Also, If you are going to a big box store, take your stock spindle mount with you just in case you want to test a cheap generic rotary tool for fit.
Also, people seem to really struggle getting routers and spindles into their mounts. You simply put a wide screw driver in the crack and pry it open. Seems obvious, I know, but there are a surprising number of questions about “…why won’t my spindle fit?”