The BEST way I've seen it done is this.
Look around at some tgp's that have a similiar theme to yours, or the content that you want.
Take note of the galleries that are listed frequently at a lot of places. They're obviously going to be trusted.
Either contact the tgp owner for the submitters info (making another contact for future trades perhaps), and/or use whois to see who's submitting.
Send out an email to those that you want to submit to you. Whenever I've gotten a personal email along with an instant partner account, I'll usually throw it on my submit list.
