With the Ricoh GRD IV, the Ricoh GRD line is dead. There will be no more produced. It has been replaced by the Ricoh GR line of cameras, so if you are looking for the best Ricoh GRD IV alternatives, here are some options.
The truth about Ricoh GRD IV alternatives
Before going into some of the options available to you as alternatives, let me make a point: There IS no proper Ricoh GRD IV alternatives. Yes, you've heard that right, there are similar cameras, but none will replace the GRD IV, I've shot with one for YEARS and I could never replace it. The only replacement for the GRD IV is the Ricoh GR camera, but it is a large sensor camera, so you'll have to be ok not having the small sensor camera look.
If you however go out of your way and get another camera from another brand, they are usually not that pocket friendly and don't have street photography features like snap focus.
But let's face it, the GRD IV is getting rare to find everyday, you can check on Amazon to see if there is one for sale. So here's your best bet
8 Best Ricoh GRD IV alternatives
When the Ricoh GR was being revealed, the tagline was “only a GR can replace a GR”. They are not kidding, the only thing that can top a Ricoh especially for street photography is a Ricoh. In essence this is the GRD IV, but with a large sensor (APSC size) added to it. It doesn't really feel the same, but it is the camera to get and the closest you will ever get to the GRD IV. Also has a 28mm.
In short: About the same, larger sensor, safest alternative
If you want to keep the portability, get the Sony RX100, it's well liked by a lot of street photographers and since there's lots of iterations, you wan find one that fits your budget.
In short: Larger sensor, not the same handling, newer models have viewfinder, has zoom
The alternative I wanted to suggest was the Panasonic LF1. This is an older camera, but what it has is a small viewfinder and a larger sensor size as the Ricoh GRD IV. It's a cute little camera, has a zoom and a fast wide angle. This is the one I purchased when my GRD IV died. Panasonic LF1 review here. The new version is the Panasonic ZS50
In short: A bit larger sensor, portability, a bit old, has zoom an viewfinder.
This is an absolute chunk of a beast. It's nowhere near as pocketable as a GRD IV, but it has wonderful handling and the same sensor size. The Black and Whites from it are gorgeous. Nikon p7800 review here.
In short: Same guts, chunky, great handling
The Canon S120 is unassuming but very powerful. It is probably the closest to the Ricoh GRD IV because it has the same sensor and is just as small.
In short: The closest non Ricoh GRD IV alternative
If you need a Ricoh GRD IV, get one. If you can't because they are getting rare, get a Ricoh GR. If you won't want the large sensor, get the Canon S120 or the LF1/ZS50. If you want uncompromising handling, get the p7800. If you don't mind a larger sensor then the RX100.
It's a shame small sensor cameras are on their way out! In any case if you are looking at these alternatives, you are probably interested in Street Photography. Inspired Eye has a lot of them, we have a street photography course, presets and a magazine, check them out!