Yes. Definitely call anywhere you're planning on going in advance to be sure of what they have. I wasted a trip to Tuba Exchange a few years ago even after "confirming" with the John Packer people in England what instruments were available at TE. Luckily for me that was just about a 40 minute drive each way, but it was a surprise that the manufacture/distributor thought the vendor's inventory was so much different than it turned out to be.
I've never bought an instrument from the Horn Guys, but my experience in buying accessories (especially mouthpieces, mutes, etc.) from them, and in reading assessments they've made of different instruments, is that they're outrageously honest and customer-oriented -- in addition to being extremely knowledgeable and experienced.
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)