Lazerlines has a great deal this weekend, but a number of the dealers out there have bushing sets for different pen kits available. I've always been able to find sets for any pen I am looking to build. Now, finding them on some folks' sites is a different matter as they might be hidden in with the pen kits themselves...
Have you checked Johnnycnc's site or contacted him?
Right now getting Sierra bushings for $3 is a steal on lazerlinez.
60 degree tbc bushings? I've seen Johnny's listed on a couple other sites, but never in stock.
Email him. Tell him what you need and I'm sure he will make them. He has done that many times for me.
Marksman Pens also has between centers bushings for their pens. They are both between centers and 7mm mandrel bushings combined.