You will need to use Brute Leeches to fish for them. The good news is, you don't need a Tome of Ichthyological Folklore. The bad news is, Brute Leeches attract Blueclaw Shrimp and Shadowhiskers as well. Be prepared to bring a lot of Brute Leeches.
I also suggest you use the HQ Crafted Lv 60 Gatherer gear and a Lv 60 HQ Birch Fishing Rod. Gathering Materias help immensely.
Be aware when using Patience, that both the Blueclaw Shrimp and the Dravanian Smelts are Precision Hookset fish. The Dravanian Smelt will tug harder than the Blueclaw Shrimp, but lighter than the Shadowhisker. I suggest you don't use Patience until you get a feel of the tugs the three fish give, to maximize your Patience HQ output for your Red Scrips.
Also, be aware that they spawn more frequently in Fair Skies and Clear Skies. Their spawn rate drops in the other conditions.