Hey mate you need a 16mm board depending on where you live Kaidomain is a good place to buy DTP LEDs, You can also buy them from International outdoors and Fasttech should be cheaper shipping to you than buying from USA.
Beam pattern and output will probably stipulate what LED you buy i will just add a link of an example. This would be a similiar setup to your BLF A6. There is a code (BLF) it gives you 5% off. I think there may be an active 10% coupon still I’ll try and find it.
http://kaidomain.com/Flashlight-DIY-and-Tools/LED-Emitters-or-LED-Star-on-PCB/CREE-XP-L-Series-LEDs/Cree-XP-L2-HD-V5-3A-Neutral-White-5000K-LED-Emitter