How to get 100 yen coins

Yeah so I'm going to Japan soon, and I was wondering how can I get 100 yen coins? I want a lot of them because I'm planning on buying things from those little toy machines (No idea what they're called in English lol) and I see that they cost around 200-500 yen so I'll need plenty of 100 yen coins. When I exchanged currency in my country, my bank didn't have 100 yen coins, so is there some machines in Japan where you can exchange your bills to small coins?

If you can get to an arcade/ game center, you can find note to coin exchange machine.
Or you can drop by the bank and request for coin exchange. Some bank have coin exchange machine.
Worse come to worse just buy small cheap thing and pay with note to accumulate coins.
Most gachapon/capsul machine accept 100yen coin only.

When buying a 130 yen thing, remember to put in 530 or 1030 instead of 500 or 1000 whenever possible (this also has the added benefit that you don't accumulate 10/50 yen coins).

If meant Capsule Toys are calling
Gacha-pon/ガチャポン,Gashapon/ガシャポン or Gacha-Gacha/ガチャガチャ.
https://en.wikipedia.org/wiki/Gashapon
"Gacha/Gasha" means sound of toy machine lever screwing.
"pon" is "out!" sound.
Calling "Gacha" only enough.
https://youtu.be/jt2g7Fpu_58
(a bit old 2013 was 5% now sales tax is 8%)

This is last year's.
https://youtu.be/Tl0KBtX-yHk
Guys loves "one punch man(in Japan One-Pun man)",
Girls loves "Osomatsu-san".

Exchanging machine is calling "両替機/ryou-gae-ki"
standing near play area usual if larger numbers machine shop.
http://www.all-nationz.com/archives/1058037375.html
https://goo.gl/xqad34
機 is short of 機械/kikai(machine).
(No handling charge 1000Y bill will be Ten 100Y coins back)

Calling 100 Yen coins most Japanese calling "hyaku-en dama" but only "hyaku-en" enough usual.
"dama(tama/玉 based)" means shape of circle and precious treasure.

Yep, change machines in arcades are your best bet!

Oh! And two years ago I found a shop in Akihabara (I think in a building called something like Akiba Zone) which basically just sold capsule toys in bags on the shelves, thousands of different ones where you could see exactly what you were getting. Kind of like a trading card shop, but for those little toys! Some were more expensive than others (I guess based on age, rarity and popularity), but I got some cool stuff in there!

Also know that all drink vending machines in Japan take \1000 notes, so you can always get change buy simply buying a drink. And if you're staring at a gacha-pon machine, you're sure to be near a vending machine as well.