for adjustable mirrors you want to know where to buy or who actually manufacturers them?
for buying i usually search McMasterCarr first
then i see if anybody is cheaper in price. In general though with McMaster you might pay more but quality is usually medium to the best and they deliver usually faster than most others.
in other countries, other companies that are industrial suppliers might be available. i would search a telephone book in your area first. also in many countries just asking a taxi driver to take you to a large store that sells industrial supplies and or hardware store items usually works.