Re: OK.. First lesson in LR shooting..
Several outlets carry the specialty bullets you refered to and I think you are looking for the 240 Gr Sierra MK.
There are some for sale from time to time on this forum and if you want to order some contact Troxells Sporting goods in Williamsport, PA at 570-494-1562.
You may want to contact Sierra also. They did ship direct.
The 240 Gr come 500 to a box.