Here's the complete set. They are known as the French G-perms and I got them from Sebastien Felix's page
here. Dodgy execution tips are mine.
Ga: D' R2 U R' U R' U' R U' R2 [D U'] R' U R
Start with left ring push for D', then start R2 with right index on FRD; do both R's with no regrip back to the same position, using right ring pull for second U; do DU’ as one move. Flows well, no regrips.
Gb: D R' U' R [U D'] R2 U R' U R U' R U' R2'
Do UD’ as one move with left index/ring push, during which regrip right index to FRD; after that, second U is a right ring pull.
Gc: D R2' U' R U' R U R' U R2 [D' U] R U' R'
Start the R2' with thumb on top, pulling the D with left during the regrip; push the second U with left index while doing right hand regrip to put right index on FRD ready for the R2; flows nicely from there, doing D’U as one move. Only 14 moves if you count the D'U as one.
Gd: D' R U R' [U' D] R2 U' R U' R' U R' U R2
Start with left ring push, then do U’D as one move with left while regripping right index to FRD; final U is a right ring/little pull.