Hi scott
The tubes are a problem. Piper have big problems to make them right and as I understand they had another batch of bad parts, yet i might be wrong.
Your best bet is to contact Eric Pau (Trojan Flier), this is because a tube might not match ‘a’ horn, in other words the horn and tube are drilled as a pair. When I needed to replace my horn Eric helped me and provided me with a tube that could be made to match a used horn that I bought of Webco. If this will not work for just take a very very very deep breath of air, thanks god that it is winter, order a tube from Piper and an horn from Australia and then just sit and wait for ~ 5 months.
Good luck with this
Ben