I found several trombone support options, including this Neotech grip, the Hagmann brace, the Rath brace and several straps.

After several months of use, I can confirm that the Neotech grip is a worthwhile trombone support, offering the support and ease of use demanded from a trombone hand support.<<Support>>Using the Neotech grip, I've gone from from unbearable cramping to sustainable playing.