Tiffie has the right idea. If you can't find an RDM at your level, then change your tactics. Juices are an excellent way to make up for not having Refresh. Bards can help, though their Refresh isn't quite as potent at that level. If you're missing out on the debuffs, a Bard can compensate by making the party better. Or pick up a Warrior to use the "Break" weapon skills to enfeeble the mob, or a Ranger armed with the appropriate arrows. Even Dispel isn't really needed. The majority of the mobs that most parties fight use a Defense Boost move which needs to be dispelled. Acid Arrows' Defense Down effect will quickly counter that move, eliminating the need for Dispel.
If you're finding you are having too much downtime to keep the chains alive, keep in mind that there are two parts to an XP chain. There is the downtime, which everyone is always so aware of, but there is also killtime. An XP chain is the time between when the previous mob dies and when the next mob dies. That includes downtime after the previous battle, and the time it takes you to kill the new mob. If you're having trouble reducing downtime, try reducing your killtime instead. If you kill mobs faster, you can afford to rest a little longer between fights. Plus, if you kill mobs faster, you will use less MP over the course of the battle, and will require less downtime in the first place.
Some of the best XP parties I've been in haven't included an RDM at all. Instead, we've gone overboard with damage. NIN/WAR, WAR/THF, RNG/NIN, THF/NIN, BLM/WHM, WHM/SMN is the setup I used for most of the 50's. With that much damage in the party, and so little healing going on thanks to all the NIN and /NIN's, downtime was never an issue. When you can't find an RDM next time, try picking up another damage dealer instead.
The three easiest ways to reduce killtime are:
1) Invite more Damage Dealers into the party.
2) Fight a different type of mob that is easier to kill given your party setup.
3) Fight weaker mobs. Less XP per kill, but faster kills still adds up quickly.
I have nothing against the RDM job. I've played an RDM myself to level 54. They are great to have, and do help reduce the downtime incurred by MP use, as well as making all of your fighters more effective by enfeebling the mob into oblivion. I just don't think RDM's are the instant XP-machines that so many people seem to think. You can still have a great party without an RDM at any level, at least up to 61 (my highest job so far).