Hi Arcane. Yes, there is a very simple way to trade coins for supplies. You'll notice that the buildings which produce supplies cost a lot of coins. Conversely, you'll notice that the buildings which produce coins cost a lot of supplies. Any time you have a huge amount of one and not enough of the other, you can covert them by purchasing the right buildings.
I call this balancing act the "see-saw" game. You'll know you have it right when you have both coins and supplies at a ratio you're happy with. Play this game until you have the best buildings possible. If you spend resources on anything but coin, supply or happiness buildings while balancing, you're simply delaying progress in the rest of the game for yourself.
The formulas for generating resources look something like this:
Coins = (Homes) + Time
Coins = (Lots of Supplies + Some Coins + Space) + Time
Supplies = (Supply Buildings) + Time
Supplies = (Lots of Coins + Some Supplies + Space + Population) + Time
I bolded lots of coins because that's the part of the equation you've already got. Chase down the others to convert.