John Olson can be a bit challenging to get a hold of. Rather than email, phone calls may work.
He does travel outside the country a bit, and in past years, has been away for months at a time, even in winter.
You can try calling him at 612-377-0155
When he was publishing the "SL Market Letter" some years back there was a time when he had a protege that was going to take over. For complex reasons, it never happened. But, he may be able to help you in the spring department, so it's worth a call. His hame is Dave Tobin and he can be reached at 651-216-1265. Dave now runs Tobin Motor Works and DaveKnowsCars.
If you strike out there, I'd start calling the usual gang of suspects for advice: Gernold at SL Tech, Brian Peters at Motoring Investments.
Might not hurt to also contact Jim Villers a member here who has a solid engineering perspective on many things on our cars.
As you probably know there's no shortage of firms (yes, probably a bunch here in NASCAR land) that can make springs. But they do need some data on them beyond size.
Good luck, and whatever you do come back and post your research and finding results so others can benefit.