In theory any OW airline can reissue a OWE, but lately they have been reluctant to do so. Presuming you have a paper ticket originally issued on AA you can get it reissued by BA but they will charge you an extra free of USD50 on top of the OW USD75 reissue fee. CX will also do the reissue in the US but you have to deliver the ticket to them in person (or Fedex it); probably best to fax them a copy of the ticket first (they won't be able to see the stored image in their computer system). Be aware that all segments of your ticket will be vetted for compliance with current rules, and you may need to remind the airline for the rules in effect at the time of issue of your ticket if you are depending on any old rules (this checking for rule compliance is much more thorough than it was a year ago). I've found CX to be good to deal with as they are very thorough (but they will catch any problems in your routing if you happen to have any). QF is less reliable but also less likely to catch rule infringements. I try to get my reissues done in HKG now but that isn't useful if you don't pass through there frequently (by the same token avoid LHR at all costs for reissues).