It doesn't have spot metering but with its ESP matrix metering you might not need that.
The OM-PC (OM-40).
It is ~functionally~ the same as the OM-2S but the manual spot metering is replaced with ESP metering, which does wonderful things for slide films.
So it depends on how you intend to use the spot meter. If it's to average out the scene or take into account backlit situations, you might consider an OM-PC.
But, like the OM-2Sp, OM-PC seem to have a higher failure rate and for both models there are a lot of 'parts' cameras out there. They are practically unrepairable so be careful.
Spot metering and Matrix metering is 180 degrees from each other. One you make multi spot measurement and make your own decision the other the camera makes multi spot measurement and it decides how to set the exposure. The OM-2Sp seems a good alternative or simply use the OM-2n and use a hand held spot meter.
As I said, it depends on how one intends to use a spot meter.
One needs to ask one's self what the goal is that led one to the 'need' for spot metering in the first place.
I can take a half dozen spot readings on my OM-4T, marking highlights and shadows, which could take a minute or two. Or I can let my OM-PC measure all those spots and come to the same conclusion, in a microsecond.
I offer an alternative that may well suit the OP's goal.
I agree with this advice.
A hand-held spot meter will solve your spot metering problems forever and with every camera.
As you already have an Olympus system, buy only Olympus cameras and maintain interoperability between all cameras and all lenses. In the long run this will save you more money than the cost of a hand-held spot meter.
Keeping a system consistent definately saves money and frustration in the long run. The OM-4s are readily available, and the 4T's aren't that expensive. The spot meter is a wonderful adjunct. I don't use it very much, but it sure comes in handy at times.
I have to disagree with the comments about a separate spotmeter. I've got a Sekonic that is nearly as big as an OM body, and takes as many batteries. It is very cumbersome to use, and if the lighting is at all variable (scattered clouds), it is practically worthless. There is no comparison to the ease of turning the aperture ring to align the dot to the center, all while keeping the scene composed exactly as you want it. And the OM's are not just a spot meter. They have a multi spot meter that automatically averages the readings. So if you have a problematic scene you can expose it to optimize different regions.
My learning of spot metering took place with the OM4 in 1984-1987 when I "jumped ship" to Canon. It is a beautiful camera and was a trailblazer for its time, very easy to use and understand, even if what was being displayed was quite small for its time. If it is expensive, I would say it is well worth gunning for at the expense because it has held its value very well. The alternative to the OM4 in medium format is any MF outfit and competent use of spot meter, meaning you'll need to skill up to get the best results through experience. There will be sorry times but I'm sure there will also be great times. There is no real substitute for learning through experience, and relying on a camera to do all the decision making for you can be potentially misleading.
.::Gary Rowan Higgins
One beautiful image is worth
a thousand hours of therapy.
"It is horrifying that we have to fight our own government
to save the environment."
While a spotmeter might be cumbersome and extra weight I don't find my Minolta spotmeter eats batteries with an appetite and when the camera is bolted down on the tripod, focused and image composed its a lot easier to crap the meter an do those extra measurements instead on using the camera for it. Then again, simple routine and knowledge makes up for a lot of estra gear and gadgets.