One of the bicycle shop was trying to sell me one. its something like the box behind a motorbike u see on the road but this 1 is fixed onto the handle. don think can fit alot of stuff in there jus one DSLR with a Kit lens the most.
Topeak is a pretty common brand here for bike accessories. You should be able to find the bag pictured in the link easily (or one from another brand). Topeak also has handlebar bags, as do other brands.
You can check out Ortlieb bags (pricier, but very good quality) at Fall Factor along Alexandra Rd, opp the hospital.
i use timbuk2 sling bag with insert as my camera bag..
im not sure about other sling bag but timbuk2 do provide cross strap that can be attached to the bag.. it make ur bag steadied/stabled on your back..
no problem when you go cycling with it..
I place my camera in a Daiso spongy bag and chuck it into a normal backpack. Sometimes I use a big waist pouch.
Don't like to use a saddle bag to hold my camera in case I buang and the camera buang with the bike. I reckon that I won't land on my back if I ever buang so a backpack is safer? Try biologic bike accessories. They might have what u want.