GAB rights are trading at about $0.17. seven rights plus $5.75 gets you one share of GAB. ref: www.gabelli.com/Gab_pdf/PRs/GAB_26Aug2014.pdf
(7 * $0.17) + $5.75 = $6.94/s, about where GAB is trading now.
not much to arbitrage here -- especially if you add in commissions and cost to exercise rights (if any)
note: actually, the rights are currently trading 'when issued'
good luck finding trading symbols, however.
i found GAB RW WI on interactive brokers; GAB-ctrl-rw on thinkorswim; GAB/R/WI on fidelity; GABrw on the nyse-dot-com site; i've also seen GAB.R.W or GAB.RTWI
full disclosure: i am long GAB, will exercise my rights, and plan to buy more GAB.
GAB preferreds look attractive, too (paying about 5%)
Disclosure: The author is long GAB.