I don't know if anyone else has sent out any specific parts vendors, so I'll toss this into the fray. Requires Mr Shakys filler, and prices are subject to your settings.
I'm not sure if you know exactly how cooldown and duration combine without adding the "allow_duplicates": "X" where X is a number. iirc it defaults to 0. so most if not all of your offers pop up one for each rank and refresh immediately when it expires.
duration and cooldown are expressed in daily time slots, so a value of 4 is a full day (morning, afternoon, evening, night).
duration (1,3) means the offer stays 1 to 3 time slots after appearing
cooldown (1,3) means a new check for the offer to pop up with x% chance value will be done every 1 to 3 time slots.
The game doesn't support you writing the duration or cooldown as (5,1) and actually causes CTD errors, so you should fix that.
finally, you should adjust the price mods of parts. right now it's cheaper to buy an S rank processor through your mod than a V7 processor from the vanilla offer. prices are subjet to the modder's settings, not the player's, unless the player is also a modder that comes dig into your file to change the price by himself.
Good initiative though!