This code will echo the “git clone” instructions required to clone all bundles in the index (pipe it to sh when you ensure it works):

pp ~/Library/Application\ Support/TextMate/Managed/Cache/org.textmate.updates.default \
|grep -o 'https://api.textmate.org/.*\.tbz' \
|while read url; do curl -s $url \
|tar -jxO info.plist|pp \
|sed -n 's/.*url = "\(.*git.*\)";/\1/p' \
|( read repos; echo git clone $repos ); done

Here pp is the property list tool found in the Property List bundle (under Support/bin).