It sucks when this stuff happens, but it pays to not be a pushover when you call and ask about things (that doesn't mean be a dick). And there are two sides to this...
1. With these smaller businesses, the guy you're calling is busy as fuck cranking out parts as fast as he can. Your phone call is just like everyone else's phone call asking where they are in line, and it is taking him away from making parts. This slows down production, and causes more phone calls.
2. Your phone call is just like everyone else's phone call, so it's important to ask pointed questions that make the guy dig a little deeper and find your specific invoice, order #, etc. etc...
I've been the guy running machines, at LRI, and had people call and ask about their build, or change orders etc... And I don't know the ins and outs of everyone's build/order, so when someone calls in and asks pointed questions specifically about their order, I can find mistakes. Like we thought you were waiting on X part to come in, but you actually never wanted that in the first place so we can continue working on your build...
I don't know the specifics at ARC, but I imagine your order got stuck in an eddy somewhere in order flow. Lost order, waiting on the next batch of Barlocs to run, something stupid like that.
I guess, having been on the other side of it, I'm a bit more patient. I was quoted by PVA at something like 6 weeks for a barrel last summer, and it ended up being 6-7 months because my order got lost twice. BFD, life goes on.