It sounds like you’re looking for vintage silk thread used for wrapping bamboo fly rods, specifically in size 00 or A, color Blue Grey 21. This type of thread was traditionally used for rod building before modern nylon threads became common. Here’s some helpful information:

Finding Vintage Silk Thread for Bamboo Fly Rods:
1. Specialty Suppliers:
– YLI Silk Thread – Some rod builders still use YLI or Gudebrod silk threads, though many are now discontinued.
– Rod-Making Suppliers: Check with companies like:
– [Golden Witch](https://www.goldenwitch.com)
– [Bellinger](http://www.bellinger.com)
– [Lemke Rod Building Supplies](https://www.rodmakingsupplies.com)

2. Auction & Vintage Sites:
– eBay – Search for “vintage silk fly rod thread” or “Gudebrod silk thread size 00.”
– Etsy – Sometimes has old stock from estate sales.
– Classic Fly Rod Forum – Members often trade/sell vintage supplies.

Vintage Silk Thread for Bamboo Fly Rods Sizes 00 OR A - Blue Grey #21

3. Modern Alternatives:
– Pearsall’s Gossamer Silk (used in fly tying) is a close match for fine wraps.
– Belding Corticelli silk thread (if you can find old stock).
– Size Equivalent: Size A or 00 is very fine (~0.15mm), so look for threads labeled 8/0 or 12/0 in modern terms.

4. Color Matching:
– Blue Grey 21 may be hard to find, but some suppliers offer custom dye matching.
– Try overdyeing a light grey or blue thread if needed.

Would you like help identifying a specific brand or era of thread? If you’re restoring a classic rod, some collectors may have exact matches. Let me know how I can assist further!