You mean this kind of springer fork
Forks - Springer, Fork 26", Misc. , bike, bicycle, cycling, bicycle, bike, accessories, | BikeWorldUSA | Bicycle Parts and Bike Accessories
or the kind Venice Motor Bikes sells?
You should be able to get a 1 inch head set at just about any local bike shop, that sells BMX bikes and
Beach Cruisers. Here is a link to some information on headset sizing Sheldon Brown's Bicycle Glossary Ha-Hi The thing to note is that there are several different 1 inch headsets. The one you need is probably the BMX/OPC assuming that the bike you are using has a one piece crank set? If you bike has a 3-piece crankset you would need the 1" ISO headset.
ocscully
About the only thing you're going to have to do is remove the bearing race from your old forks and install it on the springer fork, put everything together (adjuster nut, lock nut, spring spacer, top cap) then measure how much of a gap there is once the cap nut is all the way on, remove the top cap then cut that amount off the steer tube then re-assemble.
Good step by step but they've already cut the steer tube to length.
YouTube - Bicycle Parts - springer fork, steering tube, and headset installation.