Any tablets with WiDi? Yes!
Q. Are there any tablets with wireless display (WiDi) capability available out there?
A. Yes! While they are relatively uncommon, the main Windows tablet with WiDi that I know of is the Samsung series 7 tablet:

There are plenty of Miracast capable tablets and phones out there running Android (Jelly Bean 4.2 supports Miracast natively or AllShare Cast for Samsung), but WiDi is pretty hard to come by in the current generation of Windows tablets! I believe this is mainly due to Windows 8 tablets utilizing Atom CPUs isntead of ‘Core’ CPUs.
Specifically, here are the system requirements that Intel lists:
CPU
3rd generation Intel® Core™ Processor: all mobile processors
3rd Generation Intel® Core™ i7 Processor: 640M; 660LM; 640LM; 620LM; 620M; 610E; 690UM; 680UM; 660UM; 640UM; 620UM; 660UE; 3610QM; 3770T; 3820QM; 3840QM; 2710QE; 2820QM; 2720QM; 2635QM; 2630QM; 2657M; 2649M; 2629M; 2620M; 2617M; 2540M; 2520M; 2510E; 2640LM; 2620LM; 2630UM; 2610UM; 2530UM; 2920XM
3rd Generation Intel® Core™ i5 Processors: 580M; 560M; 540M; 520M; 480M; 460M; 450M; 430M; 580UM; 560UM; 540UM; 520UM; 470UM; 430UM; 2540M; 2520M; 2410M; 2537M; 2430M; 2435M, 2450M; 2467M
3rd Generation Intel® Core™ i3 Processors: 390M; 380M; 370M; 350M; 330M; 330E; 3110M; 3120M; 3240; 3240T; 3217U; 3225; 3229Y; 3220; 3220T; 2310E; 2310M; 2312M; 2328M; 2330E; 2330M; 2340UE; 2348M; 2350M; 2357M; 2365M; 2367M; 2370M; 2377M
Graphics/video card
Intel® HD Graphics
Wireless
Intel® Centrino® Wireless-N 1000, 1030, 2200, or 2230
Intel® Centrino® Wireless-N 2200 for Desktop
Intel® Centrino® Advanced-N 6200, 6205, 6230, or 6235
Intel® Centrino® Advanced-N 6205 for Desktop
Intel® Centrino® Wireless-N + WiMAX 6150
Intel® Centrino® Advanced-N + WiMAX 6250
Intel® Centrino® Ultimate-N 6300
http://www.intel.com/support/wireless/wtech/iwd/sb/CS-031059.htm