I've got a few slinging.org shirts.
Some from the wyoming slingfest in 2007 and a couple I got direct from chris - probably 14-15 years ago ?
But there's nothing current.
The shirt in the link is done by (why can't I ever remember his name ?)
Anyway it's the guy who's trying to make the moulded slings, pistol instructor in the marines.
Nice guy, haven't heard from him since I said that crowdfunding a hobby for someone with a decent well paid job, was tantamount to begging
Tact ? I've heard of it