Beef tendons are onea part of beef parts and used as a food ingredient in Japan.

I had have been looking for this foodstuff for a long time, but I couldn't find them in supermarkets andor marketplaces.

You can use "I'd" instead of "I had".

However, my friend told me that there was a steak house that sells beef tendons cheaply.

Then, I have ofAfter I startend madeking dishes using beef tendon often because it really goes well with rice, and it's so inexpensive that it only costs five dollars per kilogram.!

Beef tendons are one of beef partspart of a cow, and used as a food ingredient in Japan.

I had have been looking for this foodstuff for a long time, but I couldn't find them in supermarkets and marketplaces.

Not incorrect, but sounds unnatural

However, my friend told me thaabout (a steak house) that sells beef tendons cheaply.

A steak house is grammatically correct here, but I'm not sure what you mean. Steak houses are usually restaurants, and I'm not sure if restaurants sell raw ingredients. Did you mean the word "butcher"? Otherwise if you did mean a steak restaurant, then it is fine.

ThenAfter that, I have often madebeen making dishes using beef tendon because it goes really goes well with rice and is so inexpensive that only five dollars per kilogram.