If you can't find any on ebay, you can try www.amibay.com or www.vintage-computer.com/vcforum/forum.php

Trading isn't allowed on this site so you won't find any here.

Are you using the AWE32 under Windows to load soundfonts? The extra RAM is useless under DOS as there's no way that I've found to load any soundfonts other than the defaults.

Search for "SIMM 30" at ebay, you will get many hits.

You can get 32MB (2X16MB) FPM NON-PARITY 60NS SIMM 30-PIN 5V 16X8
for 30 USD, maybe less...

You can load up soundfonts in DOS as well, but as DonutKing said, it is almost useless for several reasons:
Only non-protected mode games can be run AND you need EMM386 and the big Creative AWEUTIL TSR. Also, you need a compatible soundfont (not ALL SBK soundfonts work flawlessly). You must rename the soundfont to one of those coded in aweutil:

Synthgm.sbk
Synthgs.sbk
Synthmt.sbk

i use awe32 on windows 98 and dos.
under windows i can load soundfont, but under dos, the game use the extra ram?
i use this pc for combat flight simulators (eurofighter2000, us navy fighter, jetfighter 3, ...).

Yes, if a game supports General Midi, GS or MT-32 (typically by selecting MPU 401 and a port, default at 330h) then you can load up a soundfont that fits into the AWE32 RAM and try to initalize emulation by AWEUTIL.

Unfortunately, the games with more professional GM soundtracks are from the Dos Extender (protected mode) era, thus you cannot use the AWE in MPU 401 emulation mode ( with soundfonts) because of the limitations of AWEUTIL.

On the other hand, most of the games from Dos Extender era will work perfectly fine from windows prompt with loaded soundfonts, so this is not a major limitation whatsoever.

And there is also this option:

Vintage PC > MIDI > Another PC with SoundFont

Requires a second PC, but that once can be modern!