Pen plotters are pretty much extinct in commercial use as far as I know. They've been almost entirely replaced by large format printers, which are also called "plotters" but are really just large laser or inkjet printers.
I just tried looking a decent amount and couldn't find anybody offering contract pen plotter services. Your best bet would probably be to write some code to simulate the way lines look with a pen plotter and render it into an image, then print it with a modern large format printer (which plenty of places offer). They generally have very high print quality and should be able to print enough detail that it'll look like it was drawn with a pen.
Edit: maybe you can use Inkscape to get the pen line effect? I've only used it a bit but it sounds like something it'd be perfect for.
Not entirely. I dragged one out of storage at work a few months back to make a run of large format ARCH D-size assembly drawings for the shop floor - no sense in buying a large-format inkjet just for this task. The machine is older than me by a long ways, but is still in good working condition. AutoCAD ships with binary drivers for most of the common plotters of the day, so there was no real effort involved in setup.
I had a good amount of fun watching it go, though as others have stated, they can take forever to run. The output is gorgeous, and generating real honest-to-goodness engineering drawings on one is a special feeling.
I have a mind to try some blueprinting with it, if I can find a source of drafting film and compatible pens.
I wasn't suggesting buying a modern plotter, I was suggesting using a printing service as modern large format printers are expensive. Similarly I know pen plotters probably aren't totally out of use, but I can't find anywhere that offers them as a service you can rent (which was OPs question).
Pen plotters have actually had a resurgence lately among hobbyists with the proliferation of affordable CNC controllers and stepper motors, but I don't think many professional shops are operating them regularly. I bet there are some artists using them however, as well as occasional users like you.
I just tried looking a decent amount and couldn't find anybody offering contract pen plotter services. Your best bet would probably be to write some code to simulate the way lines look with a pen plotter and render it into an image, then print it with a modern large format printer (which plenty of places offer). They generally have very high print quality and should be able to print enough detail that it'll look like it was drawn with a pen.
Edit: maybe you can use Inkscape to get the pen line effect? I've only used it a bit but it sounds like something it'd be perfect for.