I haven't a clue I'm afraid, but for domestic and most small business use I'm a bit stumped over why you'd want it to begin with.
Unless you live next door or on top of a tier one provider I doubt you'll find what you're looking for, although I'm more than happy to find that I'm wrong.
I'm sure you understand the way in which DSL works, which more or less governs what you get down in relation to what you can send up the same pipe.
You'd need to be bordering around or above at least half of your current download speed to get an option of 512 upload. Most providers, as you've probably found, offer ever increasing amounts of download bandwidth without increasing your available upload. Those who do offer high upload speeds do so at a comparatively high price.
Frankly, unless you are running a dedicated and quite busy web or email server (or both) I can't see why you'd even want such bandwidth.
Good luck with it anyway.