Are there any sources that give tricks using the 3 and a half clubs gaff card?

The one I have known and liked for many years is MIKO. Description below.

Six cards are placed face down on the table in a row. The magician then designates the cards by numbering them from one end to the other 1, 2, 3, 4, 5, and 6. A die is handed to the spectator, who looks it over carefully. The die is rolled, and whatever number comes up is the card that will be used. Let's say the number is 3.

The rest of the cards are gathered up and put in the magician's pocket. The spectator is asked to roll the die and remember the outcome. He is then to look at the bottom number of the die and add the two numbers, so the total is 7. The spectator is told to divide the total by 2. 3 1/2 is the answer. The magician pretends to be stumped and something has gone terribly wrong. The spectator is asked to turn the card over anyway, and lo and behold, the selected card is the 3 1/2 of clubs!

Cody Fisher's Deal Sealer

Henry Evans has one effect where he uses this and the "14 of Diamonds"

A magician from England called "Frederica" also has a routine

Bottom line is a card reveal I don't know what sort of "routine" are you expecting to find

DragonLore,

Don Alan's Big Deal uses the 3 1/2 gaff. It can be found in, "In a Class by Himself" (Racherbaumer)

On a related note is Roger Klause's Miko Revisited. It can be found in "Experts Card Conjuring." (Sharpe) A version can also be found in "The Magic of Francis Carlyle."(Pierre) This trick, while related, doesn't use the gaff, but I think the effect could be extended with its use. (Top Ch...., maybe?)

I also have a memory that Johnny Paul on the Greater Magic Video series uses it in his standup act, but I might not be remembering that accurately.
Regards,
Barry

Gaffs like these unusual values of cards are more corny than magic. But they can be used for a good laugh. My favorite is the “0” or the “½” of a suit.

I would have to agree with post above.. Cody Fisher's Deal Sealer is a great routine using the 3 1/2 of clubs.