Win7 still available?

Never liked Win8, still using XP SP3 and would like to get Win7 Ultimate (genuine copy of course) for future usage (reserved for future DIY PC builds)

However, I've been told retail and OEM versions of Win7 Ultimate has been back-ordered and perhaps discontinued... and all that's available is Win7 Home and Pro......

Is that true?  How come Win7 is being phased out this early?

So where can I still get Win7 Ultimate, and if so, for how long?
Also which version is preferred?  x86 or x64?  Retail or OEM?

All my XPs at home are genuine OEM, so for Win7, should I do the same?  What's the problem with Win7 OEM?

Can someone help me?