www.kjhowells.com will make them but will not be cheap. They do offer a DIY kit in a range of sizes and shapes and you may find one of these can be adapted. Bit time consuming to make but very satisfying. I have made two in the past.
Can understand your preferring teak, but GRP gratings are widely available and ideal for the purpose. Lots of suppliers; one example here: https://www.watco.co.uk/watco-grp-grating.html
(I've seen them much cheaper than that supplier, so worth hunting around.)