Ok I know there used to be a place near Grand Central- let me see if I can find it....
Found this on a blog Schwartz Travel is the one I was thinking of.
The longest serving luggage storage provider is Schwartz Travel Services, which has two locations:
Their main location, close to Penn Station & Port Authority, is open from 8am until 11pm, 7 days a week:
355 W 36th St.,
2F NY, NY 10018
(between 8th & 9th Ave.)
... although they claim to offer a 24hr service by arrangement, their 24hr phone number is 212-290-2626.
Their second, "limited location", close to Times Square & Grand Central, is only open from 9am until 6pm, Monday to Friday:
34 W 46th St.,
5F NY, NY 10036
(between 5th & 6th Ave.)
... it should go without saying that you MUST be sure of your times before using the limited location and be absolutely certain that you won't turn up late.
You can walk in to either location but they recommend that you email ahead to reserve your space;
info@schwartztravel.com
Again, their 24hr phone number is 212-290-2626.
Their fax number is 212-290-2656.