Source for 9 volt grain of wheat bulbs

Try eBay.  I think there are some wheat and rice grain bulbs rated for 12 volts or less.

They should be quite easy to find at most hobby shops. They are used extensively in most scales.

Or failing that, Radio Shack sell this 12v one:-

Actually, I don't normally see 9V bulbs.  They come in 1.5, 6, 12, 14, 18 V.

Do you want the bulb to be brighter?  I would stick with Lionel recommended voltage or shift to an LED.  I also believe you see a different voltage out of the board depending on whether it is in cmd or conv. 

Depending on what Williams you are talking about, the early units used 6V bulbs off a CV board, or 1.5V if it was driven off the QSI board.  I am sure there are others also if it was on track power.  I would try a 12V if you don't like the 14V.  G

I did find some 9 volt bulbs on e-bay but don't need 30 of them. Besides the seller is somewhere in ASIA. I would rather find a domestic source.

I will be going to a hobby shop today and see if I can get some 6 volt and 12 volt bulbs. Depending on the output of the R2LC at 7.9 volts I would be powering the former at over 100% and the latter at only 65%. Not much better than the original Lionel bulb that is in the engine.

Actually I did read your post and I answering along with comment about the availability of 9V bulbs.  Illumination isn't driven by voltage rating, yes applying more voltage than rated will burn a bulb brighter, and hotter, and last shorter.

Current rating/wattage matters so be careful you don't melt a shell.

If you go to Lionel parts web they actually carry one 9V grain of wheat bulb.  It will cost you the parts cost plus $9 shipping.   G

Illumination isn't driven by voltage rating

I don't understand that statement at all. If I take an 18 volt lightbulb and only power it with 8 volts it will have less that 50% of total lumen output. If I put 18 volts to an 18 volt bulb I will get 100% of the intended lumens.

Sure, but I said "Voltage Rating"  a lot more goes into lumens.   There are 12V bulbs that draw .1 amp and other 12V bulbs that draw .25 or more amps, even higher.  So the wattage is different.  Kind of like 40W, 60W or 100W light bulbs in your house.  They are all the same Voltage "Rating" but they generate different lumen and heat.

The Voltage rating is the safe voltage rating.  If you want to lower that bulb rating to a 9V and supply it at 9V it will be maxed out and not last as long. It may or may not be brighter than a 12V bulb at 9V, because that depends on the filament in the bulbs.

So you want to look at the current rating too.  A good example is the Lionel 161 wedge bulb which is 14V and .19 amps for about 2.6W.  The auto stores have a 168 wedge also a 14V bulb.  Some people just stick this in their engines.  The problem is that it draws .35amps 5Ws and can easily generate enough heat to melt the cab roof.   G

Here is what I put into my Williams Scale GG1 that was converted to TMCC Command and Railsounds 5.0.  The original headlights were very dim due to the fact that the R2LC board puts out less than 8 volts and the original bulbs were 18 volt bulbs.

Grainger 2FMG5

Miniature Incandescent Bulb, Trade Number 1408, Lamp Shape T3 1/4, Base Type Miniature Bayonet (BA9s), 1.3 Watts, 10 Voltage, 130mA Current Drawn, Average Life 250 hr., 10.056 Initial Lumens, Max. Overall Length 1.19 In., Lamp Dia. 0.43 In., Standards Meets 2012 Lighting Legislation Energy, Package Quantity 10

I have since found out that the lighting used in the Legacy K4's and Blue Comet could be used in my Lionel PRR M1a to provide a brighter head light. They are a 3mm LED without shoulder. Lionel part #620312300.

Might have to install a resister to light up the LED and another one onto the R2LC to create a power draw.

I've contacted Evans to see if their LED's are the type without shoulder.  Apparently it is this type that will allow the number boards on either side of the head light housing to be illuminated.