<p><a href="http://www.ilfordlab-us.com">Ilford USA</a> has had a lab running for a few years now. It's a bit expensive, but obviously prints on Ilford silver gelatin paper, though I think from digital scans. <a href="https://thedarkroom.com">The Darkroom</a> prints on Ilford silver gelatin paper also, and I think North Coast too. There's bunches of places. But these are all from digital files. I'm sure you could find places that would print from negatives, but then you're asking someone else to make all the creative decisions regarding the print—exposure, contrast, etc. My decision a while ago was that if I'm sending film out to get printed—color, black and white, whatever—I might as well maintain as much creative control as possible, which means having all my negs scanned at development, paying a hundred bucks to get a USB monitor calibration setup so I can manipulate color, exposure, contrast, etc. in Lightroom, and having the files printed without the usual "enhancement" that most labs like mpix like to include automatically to make the garishly bright photos that stand out to the hoi polloi.</p>
<p>So that's where I'd say an online quest for optical film enlargement services breaks down—not necessarily with the quality of the final product compared to a digital scan, but with the lack of creative control retained in that process.</p>