Re: Doesn't seem too much interest from manufacturers
500 is nothing at all, so of course the manufacturers don't care. These are mass-market products, the resellers buy that many in a week if not less.
You'd need to be asking for closer to 10,000 to get them interested.
The only way they notice small numbers like 500 is if you're a high-profile event like the Olympics or perhaps Commonwealth Games, where they can justify it as a direct marketing expense.
Also, the Android and Windows tablets have pretty tight margins, so discounts are very hard to get generally. (Apple have better margins but also have less reason to give a toss about such small numbers of devices.)