Any suggestions on where I can purchase some new ones? Or perhaps suggestions for making my own?

Mine is dry and breaking apart.

 

Check your local autopart store. I got mine from pepboys.

 

I got mine from the Lexus dealer last fall -- also replaced the rusty bleeder valves. Valves were $3.43 each, caps were $1.71 each. As Ray says, a chain auto parts store might be a good place -- probably cheaper, too. Also, the forum sponsors have lower Lexus part prices (most economical if you're already paying to ship another larger part...).