The oil pastels I use were bought at HOBBY LOBBY in their art section.They cost about $3.50 for a set of 12 sticks. I think that was about right.It's been awhile.
Yes you can mix colors ,BUT,I have some tube lures that looked great only to change color dramatically over night.I mixed some of the new colors with some that were twenty plus years old.Went from tan,to green.I find that that was my worst failure.I recommend trying the flourescent colors,you can add them before you heat the plastic.I made some tubes that had a body of charteuse,a black back,and a flourescent red belly.There was no bleeding to other colors.I placed them in a baggie of white lures,and left them in the car on a warm day,to test if they would transfer to the white.They didn't and that is a improvement on dyes,unless I got ahold of bad dye.
If you send me your e-mail address,I will send some pictures of the box of oil pastels,and the tubes.I have to use my cameras program to send.Sorry.