I'm big on buying online since we live in a really small town with basically nothing BUT a wal-mart.
I found this website that has a big bag of 30 marshmallows (pink and white) for $5. They're BIG though, so that might not help.
https://www.candywarehouse.com/marshmallows.html
Otherwise, I know that Jet-Puffed sells the pink-strawberry marshmallows closer to valentines day. HTH!
Not sure if this will work and may sound odd but maybe try using jello mix? Start making the jello, a packet of some red, hot water and cold water then add the marshmallows put them on wax paper and let dry. Maybe it will work maybe not. Or just see if they put them out closer to valentines day
Re: where can i buy pink marshmallows?