I have 22 different sets of bushings or mandrels on hand for my turning projects .... bottle stopper, razor handle, and 2 jewelry mandrel sets, so 18 different pen bushing sets, plus the 7mm mandrel bushings that came with my pen mandrel.
This means that I have the bushings needed for 19 different pen kits, possibly more if they double up, which some do ... I know my 30 cal PSI bushings can handle multiple pen styles in addition to the bolt action kits I've done.
I tend to buy just a few pen kits to make and sell, typically for myself or as a special order item from friends and family, so I don't keep a lot on hand ....
That having been said, I've recently found a few kits out there that were a great deal or bargain that are also excellent finished kits.
The Le Roi Elegant in chrome/black chrome was being sold out in 5-packs for 25 dollars a pack ... an excellent pen with a beautiful finish. I managed to grab 2 packs, and I've made 3 pens from it. This one was NOT the V2 or the "Long Barrel" ... it's the older one with the slightly wider barrel, so you'ld need to back-paint the blank or paint the barrel so it won't show through on acrylics. The barrel gets turned very thin, so blowouts may be common with this, but I enjoy the challenge and it's a very nice pen when completed.
The Slimline and Funline style pens are very cheap and easy to make. Excellent for showing off a wood or acrylic blank, and they fit nicely in the hand. I have some leftovers of a 25-pack in gold finish and a 10-pack in gunmetal finish that I got through a program meant for "Turning for the Troops", and while I occasionally turn a pen for a friend using these, I much more often turn a pen for the troops. Rather than send the pens on to be distributed through the usual system, however ... I live right next to Ft Sill, in Oklahoma. I like to personally hand the pens out to the troops. I think I have about 20 of these left, at the moment.
Most of the rest of my pens, I got as a 1-off or bought them as part of a "starter set". In reserve, I have 1 PSI Dragon pen in Antique Bronze, 2 platinum finish Sierras, a full size PSI Majestic, 2 PSI Majestic Jr - all 3 Majestics are in Rhodium/TiN Gold... I also have a spare PSI Bolt Action in Gold and an Antique Nickle Lever Action pen. I also have 3 Breast Cancer Awareness pen kits still laying about that I haven't turned yet. Those are popular with the ladies and girls year round, just cuz they're so pretty. I think I missed a few here and there .... oh, and another click pencil kit in a slimline style that I haven't turned yet.
All in all, I have less than 50 kits around the lathe.