Front axles don't break often and as they are symmetrically loaded w/o some unusual event I would consider looking at the bike's use history. Has there been an impact involving the fork/front wheel? Are the fork drop outs parallel to each other?

I believe these axles are 9mm x 1mmpt, very common. A good condition used one should not be a concern. However the condition of the axle cones needs to be assessed. We don't know for how long the axle was in use while broken and thus how long uneven wear would have been happening. It is the cones that are rather specific and if these are damaged (but the hub shell surfaces are still worth using) then take care in subbing other then OEM cones. Andy