Are you talking about a generic bobber seat or a stock marauder seat?

The generic has front pivot and rear springs, the marauder normally just bolts up.

For the front pivot, you can get a U bolt clamp type, the clamp has nearly the same hole to hole spacing as the tank mount.  So use this instead of the stock tank mounting plate or on top if that suits you.  for the rear spring you need to make a plate with the same spacing as the seat or the springs will be twisted.  Mount that to the frame with large sheet metal screws, or self tapping.

Hi its a stock marauder and was looking to attach springs to it ..I ain't no mechanic and all my ideas are from looking at possibility but not really knowing if they wold werk..on the frame under the seat there are hollow up rites were I think underneath the rear mudguard bolts to..was wandering if poss to tap these hollows and bolt springs there and then to seat if that makes any sence..if any of you hav foto of wot u dun can please share wiv me