Gumtree etc but be careful of scams due to lockdown etc. I saw some horrible gear for silly money.
At that weight it’s worth buying new. But if you go look at them check for chips and scuffs where they’ve been dropped or rust. Any which feel comfortable are fine.
Lots of steel places now make weights and pull up stations etc so you can try there too if any are close by.
I’d also recommend kettlebells if you’re using that sort of weight as they are fun and you can do more with them in my experience