You'll be lucky. You could try looking at some of the mini-big pit reels that sometimes scrape in at just over 500g. There's one that
scrapes in at slightly less (445g) due to the lightweight material used. The snag is that a relatively small weight saving costs a fair wedge.
The new Fox FX11 might also be of some interest, though it is supposed to be closer to 600g than 500.
What I will say about such reels is that, at first, they seem massive. They have a strange way of shrinking as you get used to them. I'd also suggest that you don't worry unduly about the weight of them. For the carping, piking or big river barbeling that they tend to be used for, they are going to spend most of their time on rests. The rest of the time they'll be chucking fairly unsubtle terminal tackle, reeling it in or, hopefully, playing decent sized angry fish. You aren't generally concerned about the balance of the reel/rod combination if using such tackle.
---------- Post added at 14:27 ---------- Previous post was at 14:25 ----------
I need the size, I think, for a long cast and fast retrieve when spinning off the the beach for mackerel and bass and the Daiwa BF 5500 I have weighs a ton with the constant cast and retrieve.
Ah makes more sense now. Would you not be better served with a multiplier?