Adding a Random component to CBC MAC in order to enlarge the tag space CBC MAC that is using AES as the underlying block cipher, has tag space of 2^128. If we add a random single block, concatenating it with the tag, and encrypt it again in AES CBC mode, with additional key, we get a 256 bit tag of 256 bits space:

TAG = CBC_MAC(K2,CBC_MAC(K1,M)||r) || r 

(where r is 128 bit random number) This is a randomized MAC generating tags in the space 2^256. In the same way we can easily generate tag in any size. Is there any standard that is using this method?

Thanks
First, don't roll your own crypto.

Second, why would you want to use CBC-MAC, if you have GMAC (GCM-mode) and CMAC and even better HMAC? (all of which are better than CBC-MAC)

Third, don't try to fix problems that have been fixed. (see second)

Fourth, I'm not aware of this construction being standardized and I'd doubt it has been. (see points 1 to 3)

Fifth, in fact there's a proposal that is similar to yours. Look here