Something apparent in your photos made me wonder, does your lake have a stable overflow...
If your water level is going to fluctuate widely through the year that can present a severe limitation on what plants can thrive.
When you can determine your water level fluctuation you can then think about planting stuff that stands some chance of reliably thriving and getting diversity of habitat working for your priorities, not against you.
A fundamental principle of aquatic planting is grasping
1) The deep water aquatic zone (reliably submersed in fertile water with adaquate light) -say 1' to 4' deep (any deeper and not much grows or is accesible
2) The marginal zone (soil constantly saturated with water) -at water level to about two foot deep
3) The bog zone (soil constantly wet, but not saturated) -from water level and above
Additionally you need to take several ph readings through the day from any obvious influences, to determine the basic water type, that can seriously affect what grows, check to see if you have extremes like acid water coming off pine woods, is your normal water high or low ph.
A few litmus test strip kits cost a couple of bucks from sciplus.com can figure out a ph profile for the seven acres, taking readings early and late in the day should indicate what 'type' of water you have
When those zones are reliably identified, then you can plant stuff that will thrive in those positions
As for sources, I can only refer to the one good contact in the one large scale aquatic plant wholesaler who gets me stuff at trade prices, otherwise I'm at the mercy of the retail trade, just like you. If you form a viable wishlist I can put out feelers there.
Ebay is good for picking up dribs and drabs to 'make a start' ....generally to pick up plants to start colonising a water garden it's fairly hard to beat that.... Probably way to go for you to put a range of plants in to 'test' your positions when the water margins are stabilised, before placing bulk orders anywhere.... it might take a month to 'test' a range of plants and measure if they will 'take' ....that will reduce serious losses if your water level, soil or water ph is variable
Being active on message boards usually means I get to know real good collectors and can get more stuff than I can use, so the notion of 'buying' plants from retailers is virtually irrelevant to me.
With having several acres here, planting them with aquatics, I'm more interested in what grows well here that fetch a good price in the long run, so I'm into making ponds, and planting them
I find cutting grass boring lol
Regards, Andy