For a quick answer, José's is pretty good. As a teacher, I know this offhand, but I’ll refer you to the Oxford Dictionary (online), where we have a few different pronunciations for “and”, depending on how reduced it is: Pronunciation /ənd//(ə)n//and/ Note that the stressed form, /and/, is modern RP (“Standard British”) — in American, it would be /ænd/ or /eənd/. The same dictionary gives us various pronunciations for “a”: Pronunciation /eɪ//ə/ Note that /eɪ/ is only used when the indefinite article is stressed, and only by some people. Personally, I say /ʌ/ for the stressed pronunciation. Anyhow, the reduced pronunciation of “and a” would be /(ə)n(d)ə/. Let me know if you need further clarification or if you’ve understood. https://en.oxforddictionaries.com/definition/and

As an American speaker I tend to say something like "and uh" or "end uh" or "enduh". Gee, that makes me sound ignorant; maybe I shouldn't post this.

From my American background, I analyzed how I say "and a" when I say it quickly. For example, when I say "one and a half", it sounds like "one-in-a-half". So, you might try saying "in a" quickly in order to say "and a". You can also think of it as "en a" instead of "in a". I think either way works.