"NBOME Update: Eff. 7-1-16  Candidates will be limited to 6 attempts at any COMLEX-USA examination"
http://www.fsmb.org/usmle_eliinitial.html
The FSMB site has "STATE-SPECIFIC REQUIREMENTS FOR INITIAL MEDICAL LICENSURE" which also gives the limit for the number of times you can take Level 3.
Alaska: 2 attempts per COMLEX Level 
Arkansas: 3 attempts per COMLEX Step 
Illinois: 5 attempts at COMLEX Levels combined
Indiana:  5 attempts per COMLEX Level
Iowa:  6 attempts at both COMLEX Levels 1 and 2; 3 attempts at COMLEX Level 3.
Kansas: 3+ attempts at USMLE Step 3 or COMLEX Level 3
Kentucky: 4 attempts per COMLEX Level
Louisiana: 4 attempts each at USMLE Steps 2 and 3 or COMLEX Levels 2 and 3
Maryland: 4 attempts at each USMLE Step or COMLEX Level
Massachusetts:  3 attempts at USMLE Step 3 or COMPLEX   (hum.. that sounds harder than the comlex...

 )
Missouri: 3 attempts on COMLEX 
Nebraska: 4 attempts+ at each COMLEX Level
New Hampshire:  3 attempts at each USMLE Step or COMLEX Level
North Carolina: 3 attempts per COMLEX Level
North Dakota: 3 attempts per COMLEX Level
Ohio: Four attempt limit on each Step or Level on USMLE or COMLEX
Oregon: 	3 attempts at USMLE step 3/COMPLEX level 3. 4 th attempt after additional one year postgraduate training.
Rhode Island:  3 attempts at each COMLEX Level
South Carolina:  4 attempts per USMLE Step and COMLEX Level
South Dakota:  	3 attempts per USMLE Step and COMLEX Level
Utah: 3 attempts at each COMLEX Level
Wyoming: Seven total attempts on USMLE or COMLEX in seven years