@maria a more common anglicized spelling you will often find is tie guan yin otherwise called, The Iron Goddess of Mercy. This may be why any internet searches you tried weren’t much help.
Tony Gebley once wrote a little blurb about it and describes the Monkey Picked part. I also found a generic website that also has a longer write up about it all here.
Without making any endorsements at all, here are six online retailers that sell it. I found them through Google and list them in no particular order. Quality and value may vary. No doubt there are others.
Samovar Teas
Aroma Tea House
The Fragrant Leaf
Teavivre
Imperial Tea Court
Red Blossom Tea Company
If you end up ordering some, I’d be really interested to know which one and what you thought of it be sure to come back and let us know how it went! Of course, I’m most interested in finding out how it lives up to the memory and if it satisfies a 20-year-old craving. 😉