The stores I deal with don't sell them. Same thing with the Danscos. They want you to just buy a new album. You can buy individual pages for the Danscos and get new slides that way. What I did was get some clear sheets and cut my own. Then I got some used Whitman classic albums for a buck or two each and picked out the best slides. You may find that some are interchangable from an album for another denomination. However you do it you may end up with useless leftover materials.
I will give you a different idea. Buy an album from "The Coin Collector". They are green and I have seen them new on eBay for about $10 and I think I have seen them at coin shows (but did not pay attention to the price). Anyway, the slides are what I believe to be identical to Dansco (and I believe Whitman) slides. They may be a little longer (use scissors) and they have both ends rounded which is a definite plus to me.
I bought some super size flips for medals. That material might be suitable for album slides. Another possibility might be currency holders or sleeves. A "scrapbook" shop might have archival page sleeves for 8" x 11" or 8" x 10" size, though make sure they don't have PVC on that kind of stuff.
There's an advertiser here on CT...www.thedanscostore.com It pops up at the top of the page many times...I'd check with them.