Your best bet aside from buying from a dealer will be eBay. Either way, it will add up quickly.
That being said, there are a few people I have seen that have completely replaced the stock headlight and housing to turn the bike into more of a cafe racer look. Might be worth looking for their posts (think I only saw their posts on facebook, dont think they are on this forum) and contacting them.
2016 CTX700 DCT ABS (His)
2016 CTX700N DCT ABS (Hers)
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Rear Electrical Harness Adapter