quiet, your spot on about the lack of diminutive FW800 offerings these days... your best bet would probably be to hit up eBay for a used/refurbished Lacie 'Big Disk', either in the size you'd like or the cheapest you can find and just swap whatever size drive you'd like into the chassis...
also, you could hold out for just a bit longer for this...
lacie is taking pre-orders right now, smallest size available is 80GB's, and FW800 is standard, check out Lacie's website in the mobile section..