Kwags, as John says, AFV Club have a Pak 43/41 8.8cm anti-tank gun out already. It has a turned Aluminium barrel and pre shaped Brass shields and is a real nice kit. You can also get a separate kit of rounds for it and a separate accessory kit of brass spacers for the shields. See a review at:
http://pmms.webace.com.au/reviews/vehicles/afvclub/afv35059.htm
AFV plan to release a 88mm Flak 18 sometime late this year early next year. A pic of the box top for this kit can be seen at:
http://pmms.webace.com.au/newkitnews/newf.htm
Tamiya's offering is the different Flak 36 version, and while a bit dated is still okay by some manufacturers standards.