I'm pretty sure I have a ton. I also run a small eBay store, so I'm already set up to sell.
I basically bought pallets of those power supplies for... I don't know.. really cheap because no one wanted the bulk. Honestly, this was back when I was starting out selling and I shouldn't have bought them, they're huge boat anchors.
Please take a look at the picture, let me know if you see what you are looking for attached to the stack of said boat anchors. I'm about to go to bed for the night (USA, almost 2AM right now), but I'm sure we can work out something reasonable once I figure out how *un*reasonable shipping will be to get them to you.
Edit (same night after failing to go to sleep): after looking up the 6643a, now I'm not sure if the height matches any of the units I have. Pictures I'm seeing of the 6643a definitely look less boat-anchor-y than the power supplies I have. My apologies.