[Trombone-l] bass trombone solo tone mute

[Richard Lee]

I'm playing Thoroughly Modern Millie soon, and just got the book 
yesterday.  It calls for a number of mutes, one of which is the "solo 
tone" mute.  I found a Humes and Berg tenor trombone solo tone mute, but 
haven't been able to find a bass trombone one.  I've checked Hickey's, 
Dillon's, wwbw.  JoRal and Dennis Wick both make bubble harmon mutes. 
I'm wondering if that would do the trick, or if I need to keep looking.  
Does anybody have one of these elusive bass trombone "solo tone" mutes?  
If so, where did you get it?  Thanks!