I think the problem is that if you go through the google link, no fare class is displayed. However, if you go all the way to the payment page, you would see a “detailed fare rules” option. Click into that, you can see the fare basis code, the first letter of which is usually the booking code.

Alternatively, you can always purchase the ticket and cancel within 24 hours.

Make sure that you read the fine print though. Sometimes google will show you JL61/JL62, but on the AA link it will show marketed as AA84xx/AA84xx. In this case you will earn as if you are flying AA aircraft. If you are really buying JL flight numbers, I thought it may be better to buy it on JAL (and issue the ticket on the stock of JAL?)