I am going to be re-beam my mosquito now that the hulls are almost finished, and had a couple of questions.

I can buy aluminium beam section from Capral Aluminium, however I dont think they sell it anodized.
Correct they don't sell section anodised.
I assume that it needs to be anodized so it doesn't get eaten away from the salt .
It actualy takes many years before damages is caused by corosion, if you take care with assembly using anti corrosion paste (Duralac etc) and wash down after sailing.

Any suggestions on where to get this done or where I can get section already anodized?
Do a google search for anodisers, I know there are quite a few in Melb eastern suburbs. Don't know of anywhere it can be bought anodised. Section can be sourced from assoc. through Philip Warren-Smith also I think, if you don't want to buy a full length section (enough for 3 beams if I remember rightly).

I noticed that the dolphin striker strap on this boat doesn't go the full length of the beam pads (it ends about 10cm from the outside beam hole, leaving a 25cm gap under the beam to the outside edge of the pad. I am not sure if this is intentional or not?
This is normal. Load is designed to be on rivets and inner bolt, not beam bolts.

Should I replace the strap with a longer one so that it fills the beam slots completely,
No.

Fill the void with epoxy filler, or fill it with sikaflex like it was when I pulled it apart?
I like to fill the void, with epoxy filler or similar thickness of wood is ok.

Is there any tricks to bedding the beams?
They can be completly bedded into epoxy filler, filling gap to deck at the same time, but if you don't use some release agent, could be difficult to get apart in future.

I was planning on bolting the new beams in using the existing holes,
If existing holes are sound and not out of round this is ok, but most are worn larger with time. If this is the case, fill holes completly with epoxy filler, then sit beams on and measure boat width to measurement rules, then centre lines (usualy a few mm wider at bow than transom)and diagonals to make sure hulls are aligned correctly and drill new beam holes. Then go ahead with sealing as you suggest below.

and sealing around the beam holes and outside of the beam with sikaflex. Is this correct? Do i need to put anything between the beam and the beam pads to ensure a nice tight fit?
See above.

Thanks in advance,

Andrew