You either strip you own rubber to whatever width you need, unfortunately this gets you into the one pricey toy I own for indoor flying, see: http://www.gryffinaero.com/models/ffpag ... arlan.html
for an example and plan on spending $150. If you really get into free flight indoor, it will pay for itself, but for WS... maybe get a couple of schools to go in on it?
Alternatively you find a local nut like me as sweet talk them into stripping the rubber for you, depends on where you live on how hard it is.
Finally you can buy pre-stripped rubber at http://www.a2zcorp.us
look under model supplies, indoor, rubber. He has any size you want. http://www.freedomflightmodels.com
has a couple of custom sizes in the appropriate range for SO. He also has a prop pitch gage. There may be a couple of other sources out there, but I'm not sure who they'd be.