Beltsville Rosedale Auto Electric is a full service automotive, marine and industrial electric shop in Beltsville, MD just off old Baltimore Pike.
They sell and repair both automotive and marine electrical accessories including starters, alternators, lift motors, tilt/trim motors, etc., etc.. They have a reputation for being able to locate parts for and repair unusual/hard to find items. They also stock fuses, connectors, battery shutoff switches, etc. They are also a factory authorized Bosch service center, so they should be able to handle European parts as well.
According to the manager I spoke to there, they also do conversions and upgrades, so if you need to have your stock alternator upgraded for higher output, they can handle it.
They are a fairly large warehouse operation and appear to be well stocked. Additionally, they can complete most work pretty quickly.
I dropped off an alternator for diagnosis and repair at 12 PM and got it back by 4:30 PM the same day for a charge of time and materials only (many shops charge a flat fee, regardless of what may be actually required to repair a unit).
Beltsville Rosedale Auto Electric
11292 Old Baltimore Pike
Beltsville, MD 20705
M-F, 8 AM - 5 PM