I'm going to generalize but, basically, you can put almost any window in the basement. Now, I suspect 1) your current frames are 'roughed-out' with either cement block or poured concrete, and 2) you did say they're below ground.
Start with going to the Home Centers (Home Depot, Lowe's, etc., etc..) Tell them what you want to do. There are specialty door and window shops too (but most likely more expensive.) The long and short of it is unless you're replacement windows are EXACTLY the same size as the ones you currently have, you'll have to cut the wall. In order to do that, you'll need special saws and such. It's a messy job and you'll probably have to rent all the tools you need (unless you're in the trades now.)
I wish I could say more. My best to ya and hope this helps.
Jay J -MOderator
PS: Here's one site I found on the WEB. They're out there if you know how to use a WEB Search Engine: Columbia Windows ...