Getting decent prints of your artwork is the bane of all artists. Most printing companies haven't a clue as to how to best go about it. I've actually had them tell me that a lithograph is the same as a xerox copy. I had a printer who does major publications for NASCAR and magazines in the SE US do a set of 50 prints from one of my pieces. When I went to see the results each print had lines running through it as if the rollers were dirty. I was told this is "normal" and that all their other artists accept it. I did not. Then they told me they could do a better quality print BUT it would cost me $40 PER PRINT and they had a minimum order of 1000 copies. Right-o.
So, many serious artists actually purchase their own printer and do their own prints. But, of course, large format printers are very expensive. Mike Sibley has said he had a terrible time finding someone to produce his prints with the quality he required. His are actually lithographs that are done directly from the original - which as I understand is placed on a drum for each copy. This is probably not practical for most of us though ... the rest work off digital images. (And taking good photographs of artwork is an art form all it's own!).
I think your best bet is to contact an artist who does prints. Being artists they know what you are looking for and how to get their equipment to produce it. Prints are not inexpensive this way, but you are more likely to get the quality you want. Diane Wright (www.dianewrightfineart.com
) is one such artist.