There are a number of vendors on iOffer selling the complete series (including final movie) on DVD. Though bootlegged off a combination of syndicated rebroadcasts and VHS station masters (there are alas no commercial releases), the set is fairly high quality, 8.5 or 9.0 out of 10.
All the iOffer vendors are selling the same set, despite different prices and listing copy -- once a bootleg set circulates, it can be duplicated and re-sold by anyone -- so just look for the cheapest listing. I got mine for approx. $50.
You must have better luck than me! I've been looking everywhere, including iOffer, to no avail. I thought I found one seller but when they vanished in the wind I took that as a bad sign :(