Where can I find rare light bulbs for my 83 300sd. I'm looking specifically for a 7528 bulb preferably xenon or ultrawhite for my turn signal. thanks

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W126 1983 300SD 286,000 miles and ticking
Baby blue exterior Grey MB tex
Recent work:
Replaced air cleaner mounting brackets and heat shields
Replaced alternator, fan and power steering belts
Replaced positive battery terminal
Replaced negative battery terminal and cord
New Duralast Battery

My car needs work.