So, I've finally made a decent one in EPS, which matches the computer modern join symbol to an acceptable level.
You can create save it into your Tex build directory and then define a \LJoin macro for it with
The scale is correct for whatever font size LNCS uses, but you might need to tweak it for other styles.
Don't ask how I made it, it was a real horror story, and involved far too many random bits of software.
PS \bowtie and \Join look sufficiently different than it's annoying if you mix them, so use the right one.