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Anthony NexExposures had some (I don't have a current catalog) their website is www.exposuresonine.com
Light impressions has them and are less expensive.
www.lightimpressionsdirect.com
And at the risk of offending BcD, Mark Macrae has a really nice system of mylar pages in binders. They looked the nicest of any I've seen. If you don't have his email address email me off list and I'll forward it.
Assume the high priced option you refer to is MJ Roop.