Good drainage will encourage good root development. You may get a respose from
a local landscaper if you ring round offering your flags up, depending what
they're made of. Yorkstone should command a reasonable price. Research what
local suppliers are selling this for to get an idea what price you can command
(you'll be competing with wholesalers, not retailers remember). Anyone who
wants you to pay them for removal for Yorkstone Flags is probably having a
laugh, so to speak.

Hope this helps.

Dave.