First look in your download list to see if you can get it from there.
If not I think you'll need to contact Customer Services.
I've got the same issue, Hicks997. Except, my Plus has got about 100+ days left before it expires. I purchased the trilogy when on offer, but also downloaded the first for free the previous week from the Plus section. Sly 2 & 3 have no expiration date, but Sly 1 still does. I too would like a solution to this.
I was wondering this as well as I bought the trilogy after I'd already got the 1st one on ps+, its showing an expiry date (got till start of december). will gill give sony a ring to see if they'll sort it out.