It sounds like your product is some sort of a marketplace where one side (sellers/businesses) will pay and the other side will come in free. If so that's one of the oldest games in town. And showing an angel that sellers will pay to sell/promote their product on your platform is not going to generate much excitement. (Sellers ALWAYS want to sell and will pay for customers if they see a particular system/channel working).
Your challenge will be to build up the user base quickly. Identify a segment (your customer's customer's perhaps) and offer some sort of an exclusive (you will have to pay for that discount most probably unless your sellers are willing to chip in)
If you do want to go the angel route immediately some options are > angel.co > local tech meetups > cofounders lab (I've found good entrepreneurs there)
Happy to compare notes, drop me a line at mayukhm@gmail.com
Cheers