Zhè běn shū wǒ zhǎo le hǎojǐ nián, zhēnshì tàpòtiěxiéwúmìchù.
I've been hunting for this book for years - truly a case of wearing out iron shoes and still finding nothing.
Tips
history
Popularized by the Ming story collection 《警世通言》. Nearly always quoted with its second half 得来全不费工夫 - the contrast between fruitless search and effortless discovery is the whole punchline.
usage
Functions as the setup of a two-part saying. Use the full couplet 踏破铁鞋无觅处,得来全不费工夫 when you find something easily right after giving up on finding it.