Sorry for taking so long getting back ... crazy busy.
I honestly believe you'd have a better time ... in a niche less jaded than general IM to this type of partnership, searching Alexa and Google for high ranking sites that compliment your offer ... and going after JVs one at a time. I'd have to think merchants in niches outside of IM more apprehensive to co promote with whom they might consider competition, so it might even be in your best interest to join their affiliate program, and if you feel their products worthwhile ... promote them, first.
IMHO ... in both IM and out, the best time to look for JV partners is when you don't have a product launch coming up ... no pressure, and it makes the relationship building process appear far more mutual.
However ... many IMers have additional lists in more specific niches ... announcing it to a general JV Marketing announcement list may just get you a handful of worthwhile partners.