Well, I actually am talking about a standard glock mag, 17 rounds. I have spoken to people who use custom rivets, but can't remember where they said to get them. Apparently, with the custom rivets, you don't need to file them down to have a nice fit in the mag well.
Will any type of rivet gun work....like say a CT special? I saw a little blurb on your website about pinned mags, but I think it was only for STI mags.
My advice is that I'd just get some factory 10 rounders for less hassle. Unless you really need that type of mag, (IDPA shooting in the US perhaps -) so here's my thoughts.
Back when the ban came in, someone was making aluminum plugs similar to the picture of the arredondo previously in this thread. I bought a bunch and used them to plug my G22 at the time. Riveted them in. (That Glock is not used much, rarely do I need to clean the mag) They might be out there somewhere.
A lot of people who do run the "plug" from bottom method of pinning are in a gray area as to how "permanent" it is - with thier various methods of locking the plug, but I've never seen any of them in trouble. YMMV...
The Glock mag spring runs fairly tight to all mag walls, so your only reliable option is something that comes up from the bottom because anything that comes in from the sides or back could bind the spring. (STI / Para / Lg frame Tangs all have springs that float in the bodies and can get around a rivet or plate. )
Even Glock tried a couple of methods of pinning those mags until they came up with the current version.
I gave up on pinning small frame Tangs and GP6 mags - it's too much hassle compared to a factory 10 rounder with dents. The 2011 modified mags I currently sell have been seized by one police authority and they passed muster so I'm satisfied with them.
There are two types of rivets at CT - a tapered fit and a rounded fit - perhaps your friend was talking about the tapered ones (as custom) My rivet gun is air powered because I do so many, but a CT one will do just fine.
Best of luck...