You might want to go through the for sale ads at Astromart and the Astronomy Mall for some glass.
If you really want to build a telescope, you can take that F.5 mirror and flatten out the curve a lot if the glass is what your problem is although glass really isn`t very expensive. For a first mirror, a 1/2" or 3/4" thick piece of plate glass isn`t that bad of an idea. You might want to stop by my website www.access1.net/bobmay for a mirrormaking article using just one piece of glass. I don`t know if the mirror has a hole in the middle as you didn`t say but if it does then you might want to make a secondary for it. You can do a Gregorian scope (probably a bit easier to do for the spacings) which uses a paraboloid primary and an elliptical secondary (an undercorrected parabola!). With that design, you will be able to test the probably 1.5" or so secondary mirror (depending upon the FOV desired) which can quickly be made without any real problems. The secondary will be a concave surface so the Foucault test can be done and with a curvature of about 8" (or probably less) the entire tester can be done on one board rather than the two pieces that is normally done because of the long FL of mirrors.
The design is also appropiate for terrestial viewing as the image is upright! Go find information on this not so common design and have fun! If the mirror really is a parabola, somebody really put a lot of work into making it so. See what you can do with it.