Try this site: http://www.batticdoor.com/atticstairinsulator.html I think they have what you're looking for.
I'm wanting to insulate the pull-down staircase going up to my attic. Are there companies/ stores where I can buy a pre-made/ fitted unit, or do I have to make my own?
tia for any info
Some of the premade units are pretty good. One other possibilty is to start with a good unit that seals well and is insulated from the get-go. The one I put in was somewhat pricey, but works well. Made in Sweden, seals tight, locks, and is well insulated (well, since most don't have any R-10 is pretty good in comparison!).
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013