Hi Wesley,
Either goes for Dave's option or BMSbattery you will be fine, It might take some time as they are from China. Make sure you check the polarity of the charging port when it arrives
You might need to be quick though as chinese new year is coming which delays quite a lot for the shipment.
For UK supplies Kudos seems to supply a charger for £20. You should check the charging port with them if you do not want to make your own port.
Pat