I posted this topic regarding the issue:
http://www.dakkadakka.com/dakkaforum/posts/list/706267.page
The good news is yes you can use them.
According to the lore and feedback I have received, MK III is still use for ship boarding actions only.
The older marks are kept as relics.
MK II's wore out and loyalist forces that either didn't receive enough of MK IV or couldn't maintain them, had to use what would become known as the MK V.
MK V ceased use as soon as MK
VI was made available, and then the gradual transition to MK VII.
So unless one of the Legions managed to keep enough MK II's laying around or MK IV's, the second founding would contain them, later chapters would have less so. If I had to put my money on it, I would consider that the Ultramarines Legion and it's successors had the highest chance of existing MK II's and MK IV's still in stock and granted to successors and so forth. While chapters like the Blood Angels and Imperial fists would have a handful of them left or less.
Apart from the Red Scorpions that still manufacture MK IV, it seems that all chapters have the capabilities to manufacture the older MK's but choose not to and use the most modern sets.
So you can justify using MKIII through to 999.M41 for any chapter. The rest is sketchy.