Correct me if I'm wrong, but Alliance has a chippy in the back of every issue on their "Girl Page". While it's not a poster, you can still admire the hotties for the scenic spendor they supply. Just get a bunch of back issues, tape a bunch together, and you'll have your very own one-of-a-kind popouri hottie poster. That may be a stupid idea (okay, it IS a stupid idea)but it is the closest you're gonna get, at least for now, anyways.
As for making it a poster, it's most likely a matter of simple economics and market competition. There are more bike mags so they often use a "perk" like a hottie poster to sway prospective comsumers to buy or subscribe to their magazine. It also is a considerable additional cost to print and insert 50,000 posters into a magazine. For the size of the market and subscriber base in the wakeboarding scene, it is too high a price to pay just for either magazine to print a hottie poster at their own expense. Trust me, they want to hook up their readers but it's expensive!!
Jeffrey, as for getting more women's coverage, that's where you, the readers, CAN make an impact. Find the email addresses for the editorial teams of your favorite magazines and tell them you'd like to see more women's wakeboarding in their pages. They certainly want their magazines to reflect the desires of their readers, so let them know what you want. If there's enough support I assure you you'll see more of what you're asking for.