what is a high gauge bass strings that will allow me to tune down to b tuning without the strings flopping all over the place?
130 would be a good gauge. just use strings made for a 5 string. but its never going to sound as good as a 5 string, as it wasnt designed to go down in that range. want it to not sound bad a floppy should get a 5 string bass.
You'll want a set of strings like these (RS66LH) - the gauges are essentially the same as a 5 string set but without the G. You'll want something around the .130 mark for the low B string.

It doesn't really have to be .130 either.
I use .110 and it's fine. I like a little bit of clacking though.