For tanks the ones available will pretty much all need glue and paint. There is some scale stuff out there that does not need glue and paint but that's mostly cars (Aoshima's recent 'The Snap' 1/32 line and soon they have some 1/24 stuff coming, Fujimi has been doing a number of snap 1/24 stuff as well like the FJ Cruiser). Fujimi also has a line of 1/700 scale WWII ship kits which are snap fit. Meng model has done some snap aircraft/ship stuff (1/48 Mustang comes to mind). Those are about the best I can think of off the top of my head.
For armor one of the easier ways to get into it is the
Tamiya 1/48 scale line as they are not too expensive (box is same size as an HG Gundam too) and Tamiya kits are notorious for being able to build easily. No Type 95 sadly (they are stupidly subjective what they make) and they do require glue/paint though. For glue Tamiya Extra thin or GSI Creos Mr Cement S or SP feels like cheating in a way since it's so easy to work with. Paint though can be a hassle but that's part of the fun for many. One thing to note for armor stuff too is it usually comes molded in a color that would match the tank and tanks are largely always one color. So you really could just get away with gluing them together, maybe painting a few bits here and there (Gundam markers may even be enough here) then give it a spray of flat top coat and you would have a pretty good looking kit near straight out the box.
Girls un Panzer stuff is run by Platz and they are the importer for Dragon here in Japan so they'll rebox a lot of older Dragon stuff in Girls und Panzer boxings then throw in the special decals for it. They will use kits from other makers from time to time (Fine Molds Type 95 was a recent one).
I wish Bandai would dabble in scale stuff (historically they did scale I have a 1/24
Bandai Zero fighter kit and some
1/48 Bandai tanks in the stash somewhere). Some easy to build Bandai quality 1/48th scale armor kits would be the bee's knees. But they have enough on their plate as it is at the moment.