Lite ply, plasticard etc. can be bought on line with little problem.
http://www.cornwallmodelboats.co.uk/acatalog/lite-ply.html
I have used them and I get what I order no problem.
As to scroll saws
laughs I have never used one so no ideas if I have to cut normal ply I use backed saws ( razor saws are a godsend) a tenon saw is a must have.
Cutting curves well I suppose a scroll saw would work but I hack parts out then shape them using a plane and abrasives ( I find wet and dry to last n last) files may not be a cabinet makers cricket but I use them if they seem to be a good idea.
Dremel type cutting discs work.
Sorry but I just do what I can with what I have, not ideal but I have fun and that is what its all about.