I only posted this because after finishing most achievements, this was one of the final ones I had remaining.
Although you will get this naturally through playing the game multiple times (which is quite fun!), if you are looking for a quicker way to get this -
Start your game at The Grove of Destruction (Difficulty - Weakling),
I started as the Dwarf, since a swipe or two of his axe usually kill most monsters on Weakling Difficulty.
There are two chests here that each have a ring in it for use.
After defeating D. Beast, when asked to help the Gnomes, do so.
After finishing this short level, purchase the potion to be small enough to enter the village.
The first house, which is the magic shop, is locked. Go to the second house and speak to the first person by entrance/exit who will tell you the shop is now open and you will now be able to enter the first house.
There will be 3 categories to choose from, the third which contains different magical rings.
It let me purchase 3 of each Ring, and there are 4 Rings total. If you do not have space for them, you can throw non-Ring items in the trash to make space for it.
(There is also a Challenge called Gnomes R Us for this, which is Buying an item in the magic shop in the Gnome Village.)
Use Rings as soon as you get them, even if you don't hit an enemy it will still count.
Any questions? Feel free to ask! I always give credit to anything I add through comments/messages. Negative vote? Please tell me how I can make it better! I'm open to suggestion and/or criticism, you won't hurt my feelings, so no worries!
PS - It was truly great replaying through this gem, that claimed countless quarters during my childhood!