Garlic Sauce
I use Lee Kum Kee garlic sauce, which is basically finely chopped garlic suspended in soybean oil.
Substitution
The key is to find chopped garlic that does not contain vinegar. Many types of pre-chopped garlic you can find in European supermarkets are suspended in brine. This imparts a very distinct flavour that many of my reciepies don't account for. Ideally, if you can't find an oil-suspended garlic sauce, use fresh chopped/minced garlic.