Hi Qwerk,
welcome to the forums!
I've never heard of the jam session but i do know that slingerland is back to producing drums currently. i don't know when they stopped though. I just know that they are now back..

Here's the info I found..

"Legendary drum maker Slingerland brings back USA production

Slingerland, the ultimate in percussion for over 70 years, is bringing drum production back home to America with a new line of drums handcrafted in Conway, Ark. The Slingerland USA series will feature newly designed instruments as well as traditional favorites such as the Studio King snare and the Buddy Rich and Gene Krupa sets.

The Slingerland name has been synonymous with premium quality drums throughout its long history," said Henry Juszkiewicz, chairman and CEO of Gibson Guitar Corp., Slingerland's parent company. "And the new American-made Slingerlands will ensure that the legendary Slingerland sound will inspire a new generation of legendary drummers.

Slingerland was founded by H.H. Slingerland in 1912 to produce ukuleles and banjos, and the company introduced its first drums in 1928. Slingerland USA is based in a facility previously used for Baldwin grand piano production; Baldwin was acquired by Gibson in 2001. Slingerland will continue to offer instruments made overseas through Gibson's internet-based direct sales division, Musicyo.com."