Like Shiva and got money? You can try finding these items at square-enix shop or ebay. Or at shops that sell Japanese goods, such as AnimeXtreme, which is where I got the figures and cards.

Cards
Both the FF3 Shiva artwork and FF7 Shiva screenshot are rare cards in the Final Fantasy Art Museum collections. There's also a real Triple Triad Shiva card that's pretty rare. Recently you can get a FFX Shiva portrait card and FFX Fayth of Shiva card.

Figures
The FF8 Kotobukiya figure of Shiva came in a normal and clear version.

The FFX incarnation of Shiva has several figures. The Final Fantasy Creatures collection (Vol. 1) contained mini figures of Shiva, including clear versions and metallic versions. They were very small (around 6cm) and needed assembly.

The FFX incarnation was later redone by Takeya Takayuki for the Final Fantasy Master Creatures collection. The new Shiva figure is around 17cm and has much more detail than any previously produced Shiva figure. This figure also comes in a limited version HERETIC Shiva based on Dark Shiva. Interesting to note that Shiva's legs are also crossed, Hindu style.

The FFXIII Shiva Twin Sisters were released as a set of transformable Play Arts Kai figures. They're highly detailed and in proportion to the Play Arts figure of Snow Villiers, who can be placed on them.

Shirts
So far there's one cotton large (or extra-large) shirt by Squaresoft for the FFX Shiva. It has an image printed on it of Shiva's Fayth.