If you just like the look and want it printed on photo paper then any place that prints photos should be able to do it. Once the alterations are made and the file is saved as JPEG or TIFF it will be printed just like any other photo. You will be limited to the photo paper selections (glossy, matte, etc.) of the printer. My guess is that Propics thought you were asking if they could print on watercolor paper and they can't - maybe you are asking that!!
If you do want it printed on watercolor paper to make it more authentic then you will have to search for a printing service that offers watercolor papers as an option or experiment with them on your printer at home. While I have not printed on watercolor paper at home many have with great success. I have printed watercolor filtered pictures on matte paper at home with pretty good results on an old (10 years maybe?) Lexmark printer - so I say give it a shot!
Hope this helps!