Hello and welcome to GH!
Keep in mind that the Filco keyboards are plate-mounted switches. That means, in order for you to swap the springs out, you'll need to desolder the switches from your Filco, disassemble the switch housing and remove the springs. It's a lot of work =)
Your best bet is to find someone who has a bunch of springs for sale, and just obtain them that way. Once you have enough posts, lurk the Classifieds or post a WTB thread for best results!