I spend way too much on merch in general c':
I also collect Transformers figures and my room could be classified as a Harry Potter museum >w>
You can get your merch from anywhere. Some people are more picky and elitist on the difference between official and fanmade merch but imo s'all the same as long as you obv don't support art thieves and the like. My pins and charms come from all over.
And that's the point of the 'window' in an itabag Poshi ;P
Its safe for the pins and keychains etc and itabags usually have special inserts to fasten or push everything in so you don't have to worry about ruining your bag in itself either!
You could also get a pin board with like cork material, I did that with a collection of my Harry Potter pins (
pic)