Ford Perfect, the drop in is not available seperately. In fact its securedly very tightly to the host, not easy to get it out even with some force.
Jalbam, the IMR 18500 config is when you take out the extension to save 40mm length. That's not a lot so don't do this if length is not critical. (just that some do not like the 220-240mm length of 2 x 18650 and will do absolutely anything to make it shorter).
You can get 2x Panasonics NCR18650 2900mah for usd19.99 shipped from hkequipment.net, get it from their web store as their Ebay store is quite a bit more expensive. These are worth it, they are amongst the best. Or you can go to Ebay and get the Hi-Max 2600mAH, available from Pingyi (shenzhen) on Ebay only. 6 is the most worth it, 2 is like usd15 shipped to US. They are usd17 shipped to my country, not sure why even though its closer, so it's not that worth it if i do not get the 6-pack. Just bite the bullet and get the Panasonic 2900mAH. Or if you have a purchase from Solarforce-sales you can include and tag on to the shipment (coz they will require $2 for registered shipment per purchase), get their Solarforce blue lettering 2400mAH 18650, $7 a piece. They also are very very closely matched, ended with exactly the same voltage. Very very safe once determined that they are matched, till several tens of discharges later then would they require testing for voltage again.
You can get the AW Protected 18500 since IMR are not really needed..... Too bad they do not have Panasonic 18500s. (AW Protected are pretty over-priced for the performance, CPFM is actually the cheapest already)
Or you can try the Trustfire, cheap enough to just try if you are not too particular about the capacity...8.28 shipped.
PS. Seriously, just bite the bullet and go for the Panasonics. Really really good, you are not only paying for the Made in Japan cells, but also the quality of the protection circuit. Not only do they cut in during discharging consistenly and well, they are also the only 2 cells which terminate consistently time after time at 4.22V on my DMM on my Ultrafire WF-188 charger, which my other cells will terminate at different voltages (My DMM reads slightly higher, with my experience with my other cells like SLA etc.). They are so crazy consistent that they both charge and terminate within 0.01v. Literally idiot-proof and safe for everyone's use. HK equipment also gives you FOC a nice 18650 plastic storage box, useful for taking backup batteries out to field.