Try googling for some of the kayaking or canoeing sites - can recommend http://www.bournemouthcanoes.co.uk/ few years back they posted a 15ft6in kayak via parcelforce to me up here in Yorkshire.
You certainly could buy them some years back - in fact I have a pair in my shed, but I'm hanging on to them! They were much more expensive than standard oars. The disadvantage is that the brass collars and sleeves do need to be kept very clean and lubricated to work well. Also after a time the brass collar can crack at the edges.
Yes, I've got some in the garage too, but in sets of three halves for reasons lost in the mists of time. The metal-flanged one were a bit of a pain, but the current ones that come with Avon dinghies have plastic fittings and are very good.
i bought some avon ones last summer, plastic fittings, excelent kit 50 for the pair, foxes ipswich. had to drill holes into them to fit the inflatable.
Are they for an inflatable or something solid. Gull do v nice wooden oars that break down, using a strong plastic collar and stud that works well. Not sure who stocks them where you are but you could google.
A friend with a Wayfarer adapted a big pair of sweeps fo fold down to go under the seats. He cut them in the places he had measured off the boat, banded the ends with a bit of brass, then drilled down and epoxied a 1" stainless tube into the shaft, with a corresponding hole in the other end of the shaft, then three bolts go through the whole lot to hold them together. The system seems to work quite well, and there is no play in the joind, but it is a stiff fit, and you have to line up the botl holes perfectly.
Walker Bay make them, when assembled are equivalent to full size oars, wooden with a removable rigid plastic blade, very strong and light. They don't break down 50:50, more like 25:75
Try the walker bay web site for nearest dealer. Have also seen these oars for sale on e-bay
I bought a lovely pair from the for sale on here. 2 piece wooden, perfect to fit in the boats locker when away from the mooring, we had just had a great pair of hard wood oars (very old) stolen from the dinghy while we were out sailing.