Try Federal Mogul/Sealed Power VS424 for 235 hydraulic cam engines and 261 engines.
Try VS534 for 235 Stock solid cam engines.
I do remember finding comparable valve springs in my Comp Cams catalog. Buick 455 maybe?
Here's a link to 235/261 engine specs.
http://canadianmilitarypattern.com/1960%20235-261%20Engine%20Manual.htm