[QUOTE=Napier]
Not long ago nobody would even think of a digital camera for this. Times have changed, I guess.
To get excellent quality prints approaching a yard in size would probably want a view camera, maybe a 4X5, exposing glass plates. Horseman is a major brand. View cameras up to 8X10 are pretty common and they’ve been made much bigger.
You might get satisfactory results with a medium format camera, a Mamiya, a Hasselblad, something of this nature. Pentax makes a funny looking one, fairly reasonably priced, that looks like a 35mm SLR only about twice as big in every dimension. It might look like a SciFi movie prop the first time you see one.
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I have to disagree here. Glass plates, even? You can barely get those anymore. Your suggestions are serious overkill. First, view camera gear is stupendously expensive to purchase and operate. Large format film is expensive too, and so is processing, which is hard to find nowadays and often requires using a mail-order lab to process and scan. View cameras are also much more complex than everyday cameras and have no automation. Medium format gear is more reasonably priced but still harder to use and expensive. Film, in general, is going to be too much trouble and too expensive for someone with little to no photographic experience.
For the OP’s uses, a 10+ MP DSLR with a macro lens and a copy stand will be sufficient. A D80 and the 60mm Micro-Nikkor lens, or the new 12 MP Canon XSi and the 60mm EF-S Macro lens are about $1500 US. The copy stand won’t be cheap, though, especially for a big one. The copy stand has a flat base and a set of lights to provide even illumination, and an adjustable head for holding the camera. It’s probably going to be $700-1000, depending on size and whether you buy new or used. A small one though, good for sizes around 8x10, shouldn’t be more than $400.
Overall, unless you plan on doing this frequently or have a pressing need for immediate results, I have to second the recommendation for finding a repro service or a local photographer with the ability to do large copy work. The equipment is expensive and will have a learning curve for decent results.
The OP is printing artwork, not photos, so the regular resolution needs are relaxed. The normal rule of 300 ppi for high-quality prints only applies if the source actually has 300 ppi of distinguishable detail. The samples provided by the OP do not appear to have the fine detail that photographs do, so less resolution will be required to make a good copy. The equipment I suggested will give highly usable results around 24x20, and should also give good results at the 30" size.