Where do you guys recommend finding an eye clean 1 to 1.5 carat S2 and J diamond? Would finding such stone be possible from online vendor like blue niles and james allen? Thank you.
Most of the truly eye-clean SI2 diamonds will be bought by retailers, Pricescope and otherwise, and will be what we call in-house diamonds. The other SI2s on the "virtual list" are probably not going to be eye-clean. I'd say work with one of the PS vendors to find you an eye-clean SI2 because they are more rare than they used to be. Grade creep and the desire to maximize profits resulted in labs kicking the cleaner SI2s into SI1, so there are fewer eyeclean SI2s now than there were a decade ago. (Just my opinion.)
[eta: Blue Nile is just a drop-shipper. I don't think they can offer you the inspection services you need. Avoid drop-shippers because you need personal service for this.]
1.5ct is a popular size for upgraders and anniversary rings. There is MUCH competition for 1.5ct - 1.6ct. It's also a price point where prices jump up. You might find more selection and lower prices in the 1.3ct - 1.4ct range. That's where I ended up when I bought my last diamond. Upgrading beyond that was too costly at that time. Just was not worth extra $thousands to me to hit the 1.5ct mark.
Twinning wisps are a good candidate to be an eyeclean SI2, in general, but you have to get someone to look at the diamond and verify that the wisps don't adversely affect brilliance or transparency. There is a long thread on here about twinning wisps.
Here's another diamond that's a good option for you. I haven't seen any of these diamonds in person, but I would definitely buy one. In fact, my next diamond might be a Crafted by Infinity!