Northern Low Brass (http://northernlowbrass.webs.com/apps/webstore/) has had some good-looking used instruments and deals in the past couple of years. Worth a look. A few months ago he had a four-valve rotary Miraphone Eb tuba that I was ringing my hands over. By the time I thought seriously about it, it was gone. He seems to have more tubas than other instruments, but there's a 3+1 Boosey euph there now.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)