I've seen some GI Joe figures from the modern releases used for Mando type customs, they can provide bits and pieces as well as armor. Joe's are great for custom projects and there's literally hundereds of potential donors for parts in that line going back about a dozen years or so though the 80's versions are not ones I'd use because of the old school joints being difficult if not impossible to incorporate into a modern Star Wars figures joints. Even modern ones can be a beast to get arms to work (gotta crack torsos and dremel down shoulder joints but it's do-able and very rewarding for the range of possibilities it opens) but headswaps, feet/shoe swaps, and accessories alone make them very valueable and a go-to line for creative customizing of all kinds. I have picked up dozens of them just to use for customs and since they're scaled exactly the same, lots of other people have done the same. There's a 6" heavy gunner release of a Mando by Hasbro, we might see some official releases yet in the 3 3/4" line at some point, we''ll see I guess. Also, there's enough Boba NAd Jango versions where armor differs slightly and nipping off bits and altering them through creative means will give a lot of options for things like chest and thigh armor.