How to choose bar-end shifters for a given groupset? I'm doing a few triathlons this summer, and I'm getting an aerobar for my bike.  I'd like to be able to shift while in the aero position.

I've currently got ordinary road bike bars.  On these bars are mounted a pair of '05  Campagnolo Ergopower shift/brake levers.  The groupset in this specific case is a Campagnolo Centaur, the rear derailleur is a 10-speed, while the front has 2 speeds.

I'm riding with a pair of clamp-on Profile Design aero bars.  I'll be riding solo, so I don't need (or want - my weight is quite far forward!) brakes on my bar ends.  Instead, I'd like to be able to shift from this position.   Currently, my Ergopower shifters are still hanging in front of my drops.  I no longer ride in the drops very often; I'm either on the aerobars or on the hoods when going up a hill or in a group ride.

How do I select shifters for the aerobars?  The photographs I've seen look like the old friction shifters that go on a downtube.  As suggested here, friction shifters would be difficult with a 10-speed for the rear.  Also, I rather like my indexed system: I can adjust at home, and then click and forget while on the road.  Must I use:


Shifters of the same brand as the rest of the groupset? (Shimano/Campagnolo/SRAM)
Shifters of the same product line as the rest of the groupset? (Dura Ace/Ultegra, Record/Centaur)
Shifters of the same model year or generation as the rest of the groupset?
Shifters with the same number of indices? (10 speed, 9 speed, 8 speed)
Indexed or friction-type shifters?  


I'm having a hard time finding the shifters for my system at a reasonable price in an exact match. I've found other Campy bar-end shifters, but they're all of the higher-end Record series than my Centaur system and they're usually a newer model.
You do need an indexed, Campagnolo shift set which is set up for the same number of gears that your bike has. 

Centaur is 10 speed Campag, if I remember correctly, so something like this:

Campag Record 10 speed bar end shifter

If you bike is 11 speed, then this, or similar:

11 speed Campag bar end shifter

Keep in mind that you will also need a new set of brake levers without shifters, and that most aero brake levers are set up for a bullhorn style handlebar. You may want to change that as well. 

You will, of course, lose the ability to shift from the hoods or drops. 

As for price, you should of thought of that before you bought Italian components to begin with. :)

Edit:

Must I use:


Shifters of the same brand as the rest of the groupset? (Shimano/Campagnolo/SRAM) YES, They generally use different spacing between gears (Campag/Shimano) or different cable pull ratios (Shimano/SRAM).
Shifters of the same product line as the rest of the groupset? (Dura Ace/Ultegra, Record/Centaur) No. You may mix component levels, if they match brand and index number.
Shifters of the same model year or generation as the rest of the groupset? Helpful, but with a few exceptions, not mandatory.
Shifters with the same number of indices? (10 speed, 9 speed, 8 speed) Yes. No options, unless your shifting is friction.
Indexed or friction-type shifters?
Indexed requires indexed. Friction can work with most things, unless it is designed for fewer gears. Spacing doesn't matter. 


Edit 2:

Also, for what it's worth, I can't find any Campag time trial shifters which are any group set other than Record in any of their online available catalogs. It is common to only produce 1 high end model of specialty items like that, so they may only have made Record models. Also Record 10 speed TT Shifters are discontinued, so if you really want a set, get them ordered while there are still some available.