Thsoe butt caps are from Tandy leather. They are 1' heavy duty conchs($2). They make quite a few different styles and sizes. They also make light duty but they are just stamped sheet metal where these are are cast. The cork and rings come with the grips. Here is a link to the Fishawk thread colors.
http://www.fishhawkthreads.com/thread_variegated.html
Many of the colors are a little wild but, there are some that really go well with different blank colors. Wood and Burgundy-brown blanks,
Meadow and grass-green blanks, Ocean-pacbay blue And Stone with gray blanks