This fun Love Factory cork board is offered for just 10L (great deal) inworld or on the SL marketplace here: https://marketplace.secondlife.com/p/LoveFactory-Photo-Corkboard-Fathers-Day-Box/2377796?id=2377796&slug=LoveFactory-Photo-Corkboard-Fathers-Day-Box
This looks like a fun item that you can "buy as a gift" for that special dad.
There are also a variety of special father's day cards and small gifts inworld and on the marketplace. Check out this page: https://marketplace.secondlife.com/products/search?utf8=%E2%9C%93&search%5Bcategory_id%5D=&search%5Bmaturity_level%5D=G&search%5Bkeywords%5D=father%27s+day for foods, decorations, cards, and even a cute sign someone can hold. As always SL offers a lot to chose from.
If you are looking for a SL event to attend with dad, you might consider taking him out dancing to some jazz at Phat Cats with a whole dad dedicated to that special SL dad.