Another Lowbrow Customs part in the air coming to the store in the next couple of weeks is their nice simple weld on seat spring mounts
"New from Lowbrow Customs! Mount your solo seat easily with these weld-on solo seat spring mounts. Made of 1018 cold rolled steel for easy welding, they are 1" diameter with a 5/16" shaft for the spring to sit over. They are coped at 1" to fit standard size frame tubing, but can easily be enlarged to fit larger 1 1/4" tube if necessary. They come with a pair of 1/8" thick leather washers to keep your springs from squeaking."