Can you buy a bread toaster that will make more than four slices at a time?
Brits can get a six slicer:
http://www.beststuff.co.uk/dualit_6slice_toaster.htm
That same company used to make an 8 slicer.
I grew up in a family of eight. My mom just put bread on a cookie sheet and ran it under the broiler. You do have to remember to turn it over and not let it burn.
Six would be better, but eight would be perfect. I was thinking one of those conveyor types that some shops have, but I don’t think you can get it in a reasonable size for the house.
Eight slices? Are you re-enacting Yours, Mine and Ours? 
Actually, you can get home-sized conveyor toasters that run on 120, rather than commercial-style 240 or 208 volt power.
But… they’re a counter-crushing 40-50 pounds, and by the time you got it warmed up and ready to toast, you’d have four slices done in a regular toaster.
They’re a bit of an energy hog as well - the ones I’ve seen have three power levels - completely off and stone cold, fully hot, and a more or less half-power idle. Keep in mind that “half power” is still several amps of current draw.
A much more sensible option would be a toaster oven. A whole lot of them handle 6 slices, and they cost about one-tenth of what a conveyor toaster would cost.
If you really need to crank out 8 slices of toast at a time, your best home option will probably be to just get two four-slice toasters. You probably can’t run them on the same circuit, though. If you have modern wiring, you should be able to find two differnet circuits at the countertop, but you might need to have a new circuit run in by an electrician.
Buy two regular toasters, and tape them together. Seriously. That’s got to be the easiest answer to this question.
EDIT: And twenty seconds of Googling “10 slice toaster” came up with this, among other things.