Where can I buy reliable OPK's?

Never used one because usually I rely on glow, another period app and CM but both are giving me two different ovulation days. I passed ovulation this month I'm pretty sure so I want to purchase some but I don't know where to get them? I would like ones that comes with opk and the pregnancy strip ones so I'm guessing hgc strips? sorry I'm new. It's just good to have to try to avoid pregnancy or ttc.