Why did I not think of that! 
For some reason I thought that NY UN office was my only option and they said that they can not send to Russia.
I also placed a stamp order this spring and hence got the catalog recently. The dinosaur series are so weird but I can see the potential. 
I am looking forward to “Body, Mind, Soul” stamps.
Yes they are open. But it was just so annoying and have to check ID and take photos. If you have family or friends with you, only one person goes in and you will get a visitor pass sticker and they will get wrest bands. Also no big backpacks when you do ID check.
I went to the New York UN stamp store yesterday! Got some stamps, postcards and met the mailbox. Stamp store is lovely - I wish post offices could display their offerings in the same pleasant manner. There is also a bookstore and a gift store. They have great flag postcards in the book store - I got the ones for Bhutan and Vietnam as I like their flag designs.
Last week I had the opportunity to visit the Geneva Office of the United Nations Postal Administration. The employees were very kind and I was able to buy mint stamps, first day covers and cancel a stamp on a postcard. I also sent some postcards for direct swaps as, as already happened to me in 2021 for the Sovereign Military Order of Malta, being the UN an international institution it is not considered as a state for the purposes of the Postcrossing ID.
I have to say that it was a unique and exceptional experience, also because one breathes the spirit that is also found in Postcrossing of having contacts with people and cultures from all over the world. It would be nice if, as many states have already done, the United Nations also issue a stamp about Postcrossing.
For those interested, this is their website https://unstamps.org and on my website Alberto's World inside the section “United Nations Postal Administration” you can see the photos of the material I purchased. They also have a post office in Vienna, one in New York and one in Beijing.
Happy Postcrossing 
Hi! I plan to visit the UN Post Office in NYC for the first time in a couple of weeks. Do you have any advice for a first time visitor? Did they have a good selection of stamps while you were there? Are there any restricted countries to send mail to, or is it the same as the mail restrictions for the US? Thanks so much!
Hello! Sure. Main advice would be to set enough time to go through preliminary steps - first you have to go to a building across the street from 1st Avenue to get your visitor sticker and then stand in a line to pass through security / bag scan. My visit was close to end of the day on Friday so lines were not bad at all.
The stamp store seemed to have good selection - stamps are displayed in glass cases on the walls.
UN uses USPS to send mail so USPS restrictions apply, however, to send to Russia, for example, you can just buy UN’s Euro or Swiss Frank stamps and send your mail to be forwarded via Geneva or Vienna UN post offices. Postal rates and forwarding addresses are listed here. For example, for Russia the rates currently are:
From Vienna, 1.90€ for a small letter
From Geneva, 1.80 CHF for a small letter
I sent a postcard to Russia via UN Vienna for the first time and it just arrived! I mailed it on August 7th and it arrived on September 21st.
Have a lovely visit!
THANK YOU so much for this very informative response!
Stamps are one of my favorite parts about receiving postcards, and I am EXCITED that the UN will have more than one boring stamp to choose from.
I appreciate you including how to send mail to Russia, I have a penpal that I have been unable to send mail to due to the restrictions!
Although I will only be in NYC for a couple of days, I was certain I had to make time for the UN! Even making the decision to fly out at 6am to ensure I have enough time to visit!
Thanks again!
Ashlyn
You can also buy stamps on line or old ones on Ebay, affix to cards and send them to the UN postoffice in an envelope to be marked and processed
