Can anyone tell me:

a) How you get strips of 3/4" plywood as sleepers to use on concrete, do you buy it in strips or do you have to cut them yourself and if so, how?

b) Whats the best thing to use as sleepers on concrete ( i need it to even out the floor as well)

I would like to install 3/4" solid on top of the sleepers.

Most lumber yards will have a panel saw and for a nominal fee will rip the plywood into 3 inch strips for you.
You can use shim shingles under the strips where needed to raise them to a flat plane.
Use two at each location, one from either side of the strip so that everything remains level. Drive them in until desired height is attained.

the lumber yard here wants to charge me $10 per sheet to rip it into 3" strips.

It's a pain in the neck to rip a sheet of plywood into 3 inch pieces

That's 16 strips @ 8 feet, or 128 linear feet For 10 bucks!
( Actually less strips considering the thickness of the blade )

That doesn't sound out of line to me.

Ya, its about $0.60 per cut. Its your call, but seems worth it to me. Have them just undersize the strips a slight bit so that you actually do get 16 pieces per sheet. Trying to manhandle a 4 by 8 sheet of 3/4 ply on a small table saw is not only a pain in the azz but dangerous as well.