I bought mine from Amazon, I can't find the exact same but this are very similar...

https://www.amazon.com/Resistance-Exercise-Elastic-Protective-Anti-Snap/dp/B01MR6WRT7/ref=pd_rhf_se_p_img_2?_encoding=UTF8&psc=1&refRID=528T08GBC232T7TPSB7N

I would recommend something like this.

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If you get 2 sets and have a really good place to anchor them (solid door, etc), you could actually have your own home cable machine.