Sweet peas are very easily grown from seed in a small pot on the windowsill - they really don't need any special treatment.
Failing that, avoid garden centres and try the small family run nurseries in the area.

A dozen bricks and a sheet of glass and you've got a mini greenhouse its worked for me before or as meanie says in a pot on a windowsill, you can sow direct if the conditions are right......There are two featured websites on here that i know of that sell loads & loads of scented sweetpea (crocus/suttons) proberbly all of them, just click on 'S' on the A-Z at the bottom of this page and bobs ya uncle ;-)