I'd do exactly what Jedi says above. Print out fan-made cards, pop them into sleeves that are different to your Deck and keep them in a random pile somewhere close by. When you need them, bring them out. It looks like a card, which means it's representing a monster (which is what it's supposed to do), it's a Normal Monster (yep) and it's got all the relevant text on it (although the "can only be Special Summoned by JBM" is pretty redundant).
There are at least a few topic in the General Discussion area about Tokens, and one of the more recent ones was about suggestions for what to name the Ojama Tokens, because people like to play with different-looking pictures instead of perhaps 4 identical token cards. I haven't checked, but I'm sure there'll be a topic about what description these tokens should have (with additions for "Poisonous Snake Token" and the like).
If you want to make them yourself, they're not that difficult to do. Grab a template from somewhere and go at it. Using custom tokens like these will also be a lot more interesting than regular playing cards/coins, not to mention a lot more practical.