Streifeneder in Germany has a complete set available.

http://www.streifly.de/shop%20abdichtsaetze-e.htm

When the Grob TN came out mandating positive air tight control seals "for reasons of flutter prevention" I bought the necessary tape from Streifeneder..

If there's an SB or TN it would be from DG itself so I would email Chris Klix at Pacific Aerosport if you're in North America. He's been really good helping with my club's 505-20 and 300 when we've needed parts or service. Also did a fantastic job fitting a new canopy to our Twin Acro when the original came off in flight and fell into a river (solo flight and someone forgot to latch the rear canopy...).