I don't think Synergy Glass has been made for over a decade. TL Johnson no longer makes rods, only cigars. Finding a replacement tip will be a matter of luck and persistence. In the meantime, the break can be repaired with a stent. The rod won't be perfect, but it should be close.
I've moved this question to the Rod Building section where there might be a more relevant discussion. Meanwhile, what is the rod length and line weight, in case someone snapped a butt section and has a tip.
Last point, you could contact Shane Gray at Graywolf rods (forum member
Shane here). There are mentions that he purchased the remaining blanks from TL Johnson when Terry became a full time cigar seller.
Tom