You can go to a printing business center, or where you can find big ass printers with ATF above them. Those machines have big DPI scanning capabilities, or you can put it in a normal home scanner with 1200 dpi and scan it in multiple pages, then put it together in photoshop.
Hi, nice work. I have a question to you- how did you upload this drawing to computer? Did you scan it or did you take a photo, and did you do any additional editing on computer to make it look so high-quality?