Need SL-6 Heat Riser Spring Replacement

My heat riser spring (coiled) has broke and now I need a replacement. Car is a SL-6, 225 cu, a/t, 1968 Dodge Dart 270. Where do you find/buy this spring???.

No luck on Ebay, maybe not looking hard enough. Also don't have the p/n but probably can find it with some work

Thx......Happy New Year and happy MOPARs in 2019