You can get them made if they are not readily available for purchase. . . I would contact one of our members ... rherrell ... to ask if he will make.
As a matter of fact, you don't actually need TBC bushings ......
I have been turning with the TBC method for many years and nave never bought any TBC bushings at all.
The way I do it (and many others also) is to mount your blank directly (without any bushings) between 60-degree conical centers after the hole has been drilled in the blank. Be careful to not crank up the tailstock pressure so high that you could split the blank.
It is better and safer after the tube has been glued in, but that is not essential if you are careful.
You would probably already know .... the dead center is at your headstock end, and the live center at your tailstock end.
It is essential that you have an accurate pair of calipers with digital readout. . These can be bought for around $30 or so.
Before turning the blank, you measure the diameters of the hardware pieces from your kit with your calipers.
When you are turning you gradually reduce the blank diameter .... at the ends .... to match your hardware measurements, or SLIGHTLY bigger.
You measure frequently as you approach the desired diameter.
I like to turn down to a SLIGHTLY bigger diameter .... bigger by about 0.005" or 0.006" .... this allows for sanding.
I think it is better to have a SLIGHTLY bigger size ..... it looks a LOT BETTER than an undersize blank.
I have turned dozens of Slimline Pro blanks in this way.