There is more than one way to skin a cat, the player shouldn't be forced to spam supplies in order to get money.
Well, yes there are more ways to make money.
You can either:
1) Build more Factories (linked to Money production)
2) Enact Laws that are beneficial to money production.
3) Sell excess resources to other nations.
4) Some have suggested buying discounted resources from countries which you have high "relations" with, and selling them to countries with lower "relations".
And Like some have mentioned, when CG was linked to money it was quite ludicrous the amounts of money a nation could generate. I could easily end up with almost 10 000$ in spare money. And like some have mentioned, world economics are based on trade between countries. If a country could endlessly generate as much money internally then you'd see some weird things happening.
Hope this helps,