I did some search on E-bay, however, the condition is not too good, and also normally they are selling those W30+,
which I don't think it will fit.
But anyway, thanks for your suggestion as there may have 1 on E-bay...
I think you misinterpreted my suggestion, I suggested Amazon, not EBay. There are a few Levi's jean slinks on amazon, however I'm not sure if they are the ones you are looking for. Here are some links:
https://www.amazon.com/Levis-Mens-Regular-Stonewash-34x30/dp/B0018OFKDY/ref=sr_1_1?s=digital-text&ie=UTF8&qid=1485241213&sr=8-1&keywords=Levi%27s
https://www.amazon.com/Levis-Mens-Black-Stretch-32x30/dp/B000LXM306/ref=sr_1_2?s=digital-text&ie=UTF8&qid=1485241213&sr=8-2&keywords=Levi%27s
We found 0 results for "levis 901"
That's what I got on Amazon.