I'll second the slaters stone molds. Haven't used them, but used many stones that we're made at home using the slaters molds. If you're patient, they seem to come out great.
I've got a tight sandbag at 200#, as well as a 160 and 200# keg. I find all of them harder to manage than stones of similar weight, so it's certainly an alternative if you can't get around to making stones right now. Damn 200# keg blows my mind - I can't seem to do anything with it other than pick it up and walk with it!
Like Dave said, bigger stones do seem to feel better if you have longer arms, at least for the pick. The 315 at the gym I go to is a little larger than the average stone, and actually feels more comfortable with my 6'2" frame.