I know folks have posted specific WEB sites on this forum pointing people to spiral stairs. Unless it's exactly what you want, you'll be back here asking again. Nonetheless, I'm sure you'll get a couple of suggestions. But if your tastes are varied and great, I suggest you take your favorite WEB Search Engine and type in a couple of key words/phrases and let the WEB do the work for you.
You can go to AltaVista WEB Search and key in the following (including '+' and '"'): +"spiral stairs" & +plans
Then press Search. This will produce a list of ALL catalogued WEB pages that have the phrase 'spiral stairs' AND the word 'plans' on them. From here, you can sift through the 'hits' that talke about 'spiral stairs' AND plans. Once you get to a page-in-question, you then use your Browser's 'Find' feature and look for the word, say, spiral. And away you go. It's possible that some of the hits you get are outdated and possibly not there. This is life in the WEB Search world. Best to ya and hope it helps.