I haven't found a replacement for the holder that comes with the machine, but they sell other pod holders like this one http://www.amazon.com/Presto-09402-Refillable-Replacement-Senseo/dp/B000BIU088 which let you use your own coffee, rather than the pods. Not an ideal solution but it might work.

Are you using the Senseo brand pods? I know when I use the off-brand pods that don't exactly fit right, sometimes my coffee comes out too weak. You could also try (I've never done this) putting in half the minimum level of water and hitting the one-cup button... it might make it stronger. I find the Senseo coffee to be pretty strong in general, so I tend to use the one-cup holder for one cup and the two-cup holder for two cups (one mug).

Try using the senseo brand pods and only set it for 1 cup of coffee and put a little less water in.