Replacement Gearbox 1.4TDI JHG

[xenolith05]

Hi all,
My 2008 VW Polo 1.4TDi (engine BNM / gearbox JHG) has thrown its 5th gear causing it to smash out of the end cover.
I have previously rebuilt this box (12mths ago), fitting a new input / output shaft bearing plate which disintegrated. My guess is when this happened, it damaged the 5th gear pair causing this latest problem!
I’m having problems locating a replacement JHG box so am trying to find out if there are any alternatives gearbox codes that would fit, or adaptations to other boxes (e.g. bell housing swap).
I could purchase a new 5th gear pair and end cover, but these look as though they would be a similar cost as to a complete 2nd hand box.
Any suggestions would be appreciated!!
Thanks