This is an ungrammatical idiom that is also (deliberately) confusing meanings. Broker, in this case, is a construction that is intended to mean more broke, which could be said to be meaningless, as broke, in the meaning of insolvent, not having money (implied by the preceding phrase I needed money...), doesn’t have a comparative or superlative. However, the meaning of broker as applied to the Ten Commandments is a reference to the Biblical story, in which Moses smashed the stone tablets on which they had been engraved - thus implying the meaning of broken, damaged, in pieces. This is another meaning that really doesn’t have a comparative or superlative, but the intent would be to suggest that whatever is broker than the Ten Commandments is broken into smaller pieces than the tablets had been.
Grammatically, it would be more broke if it were possible for insolvency to have a comparative; more broken if the state of being destroyed as the tablets were could have a comparative.
The intent of the phrase quoted in your question—I was broker than the Ten Commandments—is to suggest that the speaker’s need for money was very intense, more so than one is assumed normally to assume is necessary.
(@Tᴚoɯɐuo reminds me that “Sinners break those commandments in a different sense”; that actually adds another level of meaning to add to the confusion: broker, meaning more (often, frequently) violated.)