For the tunnel lights, there are a few choices of flashers available.
If it is just 2 bulbs that you need the flasher for, then I would use a #552 heavy duty flasher along with a high / low beam headlamp socket. These parts are readily available at most auto parts stores for under $20.00 for everything.
Today, there are basically 3 types of flashers....
1) Thermal electromechanical, which works on the principle of heat and cooling cycles, causing the contacts to come together, and when hot, they separate. This would be the #550 heavy duty small round canister type, or the Kay Lab flasher. The Kay Lab flasher can be occasionally found on eBay for under $25 including shipping. The #550 can be purchased at your local Carquest or NAPA store for under $15, and you will also need a high / low beam headlamp terminal connector to plug it into, which is available for under $5.00. The total investment for this set up will be $20 or less.
2) A motorized flasher that will be very accurate in synchronization, is the Cole Hersee. This will set you back around $125 or so on eBay. Occasionally, you might score one for a lot less, but it will take some looking over a period of time.
3) A solid state headlight flasher that is sold on eBay. I have no experience with this type of flasher, because I am old school, and like to listen to the "click clack" of the flasher.
There are other manufacturers of flashers that were used by the Commercial Chassis body builders, such as the McDermott 4" round canister type that Superior Coach used in the 1960's and early 1970's. These were sometimes called "school bus flashers". The McDermott unit is still available, but the price tag is staggering. I checked on them a few months ago, and I don't remember if they were a little over $200 or $300, because I had no reason to pursue the matter once I learned the price.