Most niche TGP's don't use brokers for ads, any that do are probably not going to be price competitive for you anyway. If you see a site where you'd like to place an ad, there is usually contact info on the webmaster/submit/trade page(s).
TGP galleries don't need to be fancy, basic HTML with some well worded sales text, and 12-16 nice thumbs. Here's one of my more recent efforts. Nothing fancy.
http://www.bevyofbabes.com/tgp/angel...ngs/indexc.htm
Another benefit of building galleries to submit to TGP's is that you can very easily modify them for use as hosted galleries when you do decide to launch an affiliate program. I always recommend that a new site wait on launching an affiliate program. In my opinion you'll be far better off in the long run, building up your own traffic, continuing to build up site content, fine tuning site tours etc. so that when you do finally launch an affiliate program it's about supplementing existing income not about creating a traffic base.
I've seen far too many new sites launch affiliate programs right out of the gate as a means of generating traffic, with little or no promo materials, minimal site content, etc. which meant poor conversion and retention for affiliates. You only get one chance to make a first impression, screw that up and those top affiliates will move on and won't be back when you do get things sorted.
Be patient, I think you're doing fine. 120 members after just 4 months isn't bad at all. Just keep expanding those traffic sources.