How can I find all copies of an executable name in my PATH?

I think this should work:

IFS=:
for dir in $PATH; do
    if [ -x "$dir/$1" ]
    then echo "$dir/$1"
    fi
done

type -a *

For example,

type -a python

gives

python is /Users/user1/anaconda3/bin/python
python is /usr/local/bin/python
python is /usr/bin/python
python is /Applications/CASA.app/Contents/MacOS/python

Try this builtin command:

which -a python