I don't think anyone can tell from here. Have you looked around in the garage, the basement, the crawlspace, the attic, and the like, for 'replacement shingles'? Sometimes, a homeowner is left with some extra shingles. From there, you can take a sample to a Roofing Supply House (found in the YELLOW PAGES under ROOFING - SUPPLIES.)
Or, call a Roofer and tell him you need an estimate for a replacement job with the EXACT same shingles. Then, ask him which make, model, and serial number shingle he's going to use. And go from there. If the shingles are in the shape you describe, you might want to get the entire roof replaced! If you had a decent Home Inspection, the Inspector should have told you the approximate age of the roof (or how much life you have left on it.) That is useful info.
Sorry, can't say/tell anything from here. My best to ya and hope this helps.