Tente usar -regex
find . -regex '.*/webapp/bootstrap\.php'
Isso deve encontrar os arquivos desejados.
-regex pattern
File name matches regular expression pattern. This is a match
on the whole path, not a search. For example, to match a file
named './fubar3', you can use the regular expression '.*bar.' or
'.*b.*3', but not 'f.*r3'. The regular expressions understood
by find are by default Emacs Regular Expressions, but this can
be changed with the -regextype option.