Singlespeed & Fixed Gear - Advice on changing gear ratios

Could not find an exact answer by reading forums, so here goes....Thanks for your time!

I have a flip-flop hub (on a motobecane phantom cross-uno - pretty good low-end commuter bike imo), with 16T freewheel and 16T fixed on the cog side.
Been invited to do a duathlon (first one so not going to go off and buy a new bike for it). Although the gear ratio I have is fine for commuting, 38-16 - normally I use the freewheel as there are some decent hills, I tend to max out around ~20mph. I thought a cheap way to get a bigger ratio to race a flattish course would be to add a smaller cog on the cog size (14T ?). Here's where my ignorance comes in.

Can I get a 14T freewheel? If so will it be able to go on either side of the hub I have? I know you can put a freewheel on the cog side, but it seems that the only 14T freewheels are BMX and won't go on the hub I have (chime in if this is wrong).
I guess I could put a 14T cog on the fixed side and race fixed, but I'm a wuss and like to coast. Other option is to change the front cog put I'd like to keep the 38-16 ratio for commuting.

Thanks for your help, apologies if there's already a thread that answers this.

You will not be able to put a 14T freewheel on that hub. Your choices are a 14T fixed gear cog or a larger chainring. If the bike coarse if relatively flat, it shouldn't make much of a difference if you are riding free or fixed, since you should be pedaling nearly all of the time anyway.

http://www.bikeforums.net/showthread.php/716371-Uncle-Sixty-s-Gearing-Primer-for-Newbs

Note that you can buy a 14t freewheel, but it will be metric thread. Your bike uses ISO thread. The only way to get a larger gear on your freewheel side is to use a larger chainwheel.

Note that you can buy a 14t freewheel, but it will be metric thread. Your bike uses ISO thread. The only way to get a larger gear on your freewheel side is to use a larger chainwheel.

You could, in theory, rebuild the rear wheel with a BMX flip flop hub, replace the axle with a longer one and space it out to 120-130 mm (depending on the frame), and install a 14T metric freewheel. But thats a whole lot more complex than just installing a larger chainring or using a 14T track cog.

if you think 1 tooth smaller would make a difference for you...
there is(?)/was an ac 888 (not the same as acs) english threaded 15t freewheel.
that is the absolute smallest there is other than the bmx fws that use metric threading as mihlbach & sillygollem described.
not commenting on its quality but i think you can still find them on fleabay.

How about just borrow somebody's road bike for the duathalon..would make things a lot easier and would put you on a much more appropriate bike.

Last time I did a duathalon, I borrowed a road bike and probably averaged 5-10 mph faster than I would have on my Fantom Cross Uno...