There's probably not as many outboard TV tuners as there used to be (at least it seems to me - have two projectors with older Samsung TV tuners). There's a bunch that come up on a search of Amazon. Channel Master makes this - https://www.channelmaster.com/OTA_DVR_s/336.htm
I have a ChannelMaster DVR/tuner as well as an active indoor digital antenna (Mohu Leaf if i remember correctly). This was my attempt at cutting the cord but i gave up due to family pressure and now have all this lying unused. Would be happy to let go.
I would strongly recommend an active powered antenna over a passive one as the signal reception and quality is much better. ChannelMaster is quite a decent and slim sized AVR. In my case, I didn't end up buying a hard drive to make it a full DVR - i just bought and connected a 256GB USB pen drive (they're now cheap enough), and that worked perfectly. And to be honest, that is a lot of available recording space.
Another nice thing about ChannelMaster is that the channel listing and channel info is free and you don't have to pay a monthly fee for it, unlike some other DVRs.