Off the top of my head, Squadron No. 27 had Beaufighters, and was deployed to India in the summer of 1942 - I don't have the exact date at hand. They ended up being used in ground support operations in Burma by '43.
In terms of fighters, most of what was in theater were Hurricanes at that point.
OOB in April was 11 squadrons in theatre (66 squadrons were requirement). By September there were 11 fighter squadrons (10 Hurricane, 1 Mohawk), 8 attack, Blenheim, Hudson, Wellington, Beaufighter (1 sqd of these). 7 liason and 4 flying boat SQD's.
The British *did* have plenty of fires, and the ones in the Far East consistently ranked lowest in priority for Churchill throughout the war. No one argues otherwise.
Roskill says if the Japanese captured Ceylon,
"it will be extremely difficult but not...impossible, to maintain our communications to the Middle East. But, if the Japanese capture Ceylon and destroy the greater part of the Eastern Fleet, then...the situation becomes really desperate."
Which meant the Eastern Fleet would not be risked to save Ceylon, but would be preserved to guard SLOC to the ME.
All that the Ceylon garrison needs to do is hold out until reinforcements arrive, and it's quite difficult to see how they couldn't. The Indian Division may be an unknown quantity, but the Australian and British brigades were very solid, and they would have the depth of a 25,000sq mi island (almost the size of Hokkaido) to defend in depth. Even with the securing of a port (say, Trincomalee) and some airfields, the Japanese are simply not going to be in a position to cut them off from supply and reinforcement from India - at worst, even if the Kido Butai could somehow be sustained for a lengthy period time (something they never achieved otherwise), the most the Japanese could hope for is to establish daytime air superiority over the Palk Strait and Laccadive Sea - the British could still move in a great deal at night.
Quite possible, but what I don't see is any elements of the Indian army to throw in to help them - the IA looks to have been fully or nearly fully committed to guarding the LOC to Burma along the shores of Bay of Bengal, (of which Calcutta was of absolute paramount importance). There were a couple newly commissioned divisions, but these were not properly trained or equipped.
And just how are the Japanese going to get them to Ceylon?
By direct flight for the KI-21's, by carrier ferry for the KI-27's and KI-43's. (ie, same way the British got 140 Hurricanes to Malaya by February 1942).
This assumes a long-term commitment to the Bay of Bengal by Kido Butai and Combined Fleet, though - not just a limited-time invasion support campaign.
No, it assumes no carrier campaigns outside the range of land based airpower in the South Seas, no 'Midways'.
This leaves the Americans free to launch counteroffensives later in 1942 - either in the Solomons, New Guinea, or the Gilberts/Marshalls. And it is hard to see the IJN simply ignoring that until 1943 - just as it is hard to see them not reacting vigorously to the Doolittle Raid. The reaction doesn't have to be Midway, to be sure, but it would be something.
Pin pricks can be annoying, but pin pricks can also be ignored.
Japan was at her strategic limit by the spring of 1942. The only thing that made serious strategic sense was to fortify what she had as well as possible, with no more than the most marginal rounding out of the the perimeter (such as Port Moresby, for example).
Japan was at end of her strategic limit by the end of June 4th, 1942.