You might be able to find a different algorithm, but you would need to ask whether it is doing the same job as findsignal() is doing. For example, some people might be satisfied with xcorr() https://www.mathworks.com/help/matlab/ref/xcorr.html but that does not have the same behaviour of trying to find the best possible place for the signals to fit together including stretching.
Which can be written in Matlab like so to find a similar signal to s in the vector y :
It is interesting that when profiling the above non-mex code, it is similar in speed to the findsignal.m algorithm. The buffer code is heavy on memory allocation which is slow. The rms method is not a mex code.
It would seem that there is possibly scope to improve the speed somewhere ?