2nd for starting with single body sierra style pens. I try to keep a few spare tubes for pens around if at all possible too. You can buy them pre cut in packs. I've taught loads of people and kids to make pens and a single body is easier to get started on and easier to turn because you simply have more room for error. If you turn to the diameter on a slimline you have an extremely small margin for error. Starting with a sierra style pen will give you more room in the diameter. My daughter made one when she was learning with a massive undercut but she can still use it because there was "room" on the blank. The other nice thing with sierra style pens is you can buy pre-tubed cast blanks to make too. Some retailers sell pretubed wood blanks too.
That said, the company, Berea, who launched the name "sierra" may be going out of business. You'll see that most companies and woodworking stores have their own clone of that pen because it's wildly popular to make and use. PSI calls theirs a gatsby, woodcraft calls it a wall street, craft supplies is the apprentice. You can shop those websites for other pens too.
For a shopping location, make sure to check out Exotic Blanks. (
www.exoticblanks.com) they sell from most of the major manufacturers and have a wide variety of things associated with pen making. They have years of content on youtube showing how to do various techniques and make different pens. You can find sierra styles as diamond knurl (their in house pen and it's excellent from an assembly standpoint), regency, diplomat and the PSI gatsby. Exotic Blanks customer service is excellent and you can access them through email, phone or their chat that (usually) goes directly to a human in Wisconsin. The owners are IAP members and will comment on posts here from time to time.
Lots of people have wonderful content on youtube to learn from. Two of the IAP members who I've watched are Mark Dreyer's Ten Minutes to Better Penmaking series and John Underhill has John Underhill Creations out there too.
You've already found IAP which is a huge resource of people too. I'm constantly amazed by the beautiful creations people have on the site and realize how much there will always be to learn.
