Re: What would you do?
Whatever you do, don't lose sight of this: be respectful, courteous, kind, even if you take your business elsewhere.
From what you write, it sounds like you're upset because Tim and Steve put you in the middle of their own dispute. That's certainly cause to be a little irritated because you are a customer who's only buying a fly rod. They should be the ones who know the policies and be on the same page.
Here's my suggestion: See if you can gently engage Tim (and maybe Steve) in another conversation about this but gently point out that you are being placed in the middle of a dispute between his employee and him. Let them both know your dissatisfaction and that you were poorly treated (Use the old "I-feel" statements e.g. "I felt disrespected as a customer when I was lectured for something an employee did and said was OK."
Show them, especially Tim, what you're willing to do. It sounds to me like you are willing to buy a rod one way or the other. Communicate that and your willingness to remain a loyal customer. The real prize in this is not a fly rod, but the opportunity to build/rebuild a relationship that's good for all three of you, and sounds like it has been very good till this point. It can keep being that way. Communicate to them that it ought to be worth an extra fly rod in stock.
Maybe give Tim some time to think about it after you speak with him. Let him process it. If he can;t see it then that other fly shop might be worth a visit.
This is Palm Sunday, so I'm essentially putting in a plug for the cross. You don't have to take it up, but it gives life. Take this up, and you might get a chunk of that life and blessing for yourself, Tim, and Steve. You might end up with a nice fly rod, too.