I'm looking for a japanese maple that would work for zone 6a, has a
weeping growth, a VERY large spread and grows at least 4', preferably
no more than 5' with 6' being that absolute largest I can go.

Any suggestions?

Red Dragon - you might want to get one that has been staked up a bit if you
want it a bit taller and then it will spread - otherwise it will be a classic
mushroom shape.

Kiri Nishiki may be hard to find, but spreads to twice it's height. Garnet
doesn't spread as much but grows faster when it is young.

Filigree is a nice green dissectum that spreads nicely, as is Green Cascade.