Debian Linux:

I did a search using kfind and searching in executables containing the String "TForm".

The result seems ok, but are there better ways?

... all 62 executables in /usr/bin seems to be part of Lazarus.

Something like

egrep 'Lazarus LCL: .* FPC:' /usr/local/bin/*

Once you've got the names you can use strings and pipe it through grep to get the versions used. The whole thing could be automated using find but for a small number of programs would be more trouble than it's worth.

This will also work, also detects non-lazarus binaries:

grep "FPC " /usr/local/lib/fpc/3.1.1/fpc
Binary file /usr/local/lib/fpc/3.1.1/fpc matches

as a find command:

find /usr/local/bin -type f -exec grep -H "FPC " {} \; 2>/dev/null Binary file /usr/local/bin/bin2obj matches
...

Binary file /usr/local/bin/unitdiff matches

or this to display the FPC version:

strings /usr/local/lib/fpc/3.1.1/fpc | grep ^"FPC "

FPC 3.1.1 [2016/08/24] for x86_64 - Darwin

as find:

find /usr/local/bin -type f | while read file ; do strings $file | grep "^FPC " && echo $file ; done
FPC 3.0.0 [2015/11/14] for i386 - Darwin
/usr/local/bin/bin2obj
FPC 3.0.0 [2015/11/14] for i386 - Darwin
/usr/local/bin/chmcmd
FPC 3.0.0 [2015/11/14] for i386 - Darwin
/usr/local/bin/chmls